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The Khovanov to Floer spectral sequence
1 · Prerequisites
- Abelian Categories
- Absolute and Conditional Convergence; Rearrangement; Products
- Analyticity of Holomorphic Functions; Liouville and Morera
- Approximation and Compactness in C(K)
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2 · Logical flowchart
3 · Definitions, theorems and proofs
Double branched cover of an oriented link
Definition
Assume the Axiom of Choice. Let be a nonempty finite oriented smooth link in the standard oriented three-sphere, and put . A small meridian about is the boundary of a normal disk fiber; its orientation is immaterial modulo two. The mod-two meridian character is the homomorphism that sends every component meridian to . For each , choose an oriented tubular chart, meaning a diffeomorphism from a normal disk bundle onto a neighborhood, written and respecting the core orientation. Let be the parallel longitude given by for a fixed , and set . The double branched cover is the closed three-manifold obtained by taking the connected two-sheeted cover of classified by and extending it over each with local normal-disk model in these coordinates. Give its total space the orientation for which the covering map is orientation-preserving away from the branch locus.
Definition references
Finite oriented smooth links in the standard three-sphere
The complement is an eligible connected manifold
Connected covers and fundamental-group subgroups
Ozsváth and Szabó, On the Heegaard Floer homology of branched double-covers, §§1–2
Hatcher, Algebraic Topology, Theorem 1.38 and Proposition 1.39
Filtered convergence and the scope of the Ozsváth–Szabó construction
Statement
Let be a filtered chain complex over a field with an increasing filtration and . Its spectral sequence stabilizes and abuts to with the image filtration, without any uniform bound outside the finite range . If a particular filtered complex has been constructed from a fixed link diagram, this convergence assertion does not itself identify filtered complexes arising from different diagrams.
Statement references
Facts & Assumptions
Given: A filtered chain complex with and for some finite .
A filtered chain complex has (Filtered chain complex).
A finite filtration yields a spectral sequence abutting to homology with the image filtration (Bounded filtered complex spectral sequence abuts to filtered homology).
Proof
The filtration has only the levels , so it is finite, exhaustive and separated; [F1] says each level is a subcomplex.
Apply [F2] to this bounded filtered complex. Its pages stabilize and the limiting page is the associated graded of with the filtration induced by the inclusions .
This argument identifies the abutment for the fixed filtered complex only. No map between filtered complexes for two different link diagrams occurs in [F1] or [F2], so diagram-independent filtered quasi-isomorphism type is not a consequence of this convergence result.
Existence and isotopy invariance of the double branched cover of a link
Statement
Assume the Axiom of Choice. For every nonempty finite oriented smooth link , the homomorphism sending every component meridian to is well-defined and surjective. Its connected cover extends over the link with a simple order-two branch model, independently of the tubular charts used to describe that model. If is ambient isotopic to , the resulting oriented branched covers and are orientation-preservingly diffeomorphic.
Statement references
Facts & Assumptions
Given: AC and a nonempty finite oriented link .
Alexander duality identifies with (Alexander duality for compact locally contractible subsets of a sphere). Under its local intersection description, a meridian around evaluates as on and on every with .
The first Hurewicz homomorphism identifies with the abelianization of , and reduction modulo two gives the corresponding mod-two abelianization (The first Hurewicz map is abelianization).
The complement is connected, locally path-connected, and semilocally simply connected (The complement of an oriented link is a connected smooth three-manifold).
Connected covers are classified by subgroups, and two based connected covers with the same subgroup are uniquely isomorphic over the base (Connected covering spaces are classified by conjugacy classes of fundamental-group subgroups, Based connected coverings are isomorphic exactly when their induced subgroups are equal).
The local normal-disk model for a branch component is with ; its meridian monodromy is nontrivial and its longitudinal monodromy is (Double branched cover of an oriented link).
Under , two tubular embeddings of the same normal bundle inducing the same vertical normal-quotient map are ambient isotopic near a compact core, fixing that core (Compatible tubular neighbourhoods agree near compact sets up to ambient isotopy). The relative open-set clause of The isotopy extension theorem also extends an isotopy of an ambient open set with open track near any compact subset. In the application the ambient manifold is the boundaryless , the core is the compact union of link circles, the normal identifications are explicitly equalized, and the fiber-linear isotopy consists of open embeddings after a common shrinking. AC implies the required countable choice.
Proof
Compose the Hurewicz isomorphism in [F2], the Alexander-duality isomorphism in [F1], and coordinate-sum modulo two on . The local intersection description in [F1] sends a meridian of to , whose coordinate sum is modulo two. This defines and proves it is surjective because ; hence its kernel has index two.
An ambient isotopy from to restricts to an orientation-preserving diffeomorphism of their complements and carries each meridian class to a meridian class. It therefore carries to .
By [F3] and [F4], the index-two kernel determines a connected two-sheeted cover. On a punctured tube around , its two monodromies are the meridian value and a longitude value . The local model [F5] has exactly these monodromies, so covering classification identifies its punctured part with the restricted cover. Attach its core to obtain a smooth extension in the chosen charts. This constructs an extension; independence of the smooth total-space diffeomorphism type requires the normalization below, not merely equality of boundary monodromies.
Compare two oriented tubular charts around the same component. Express them over a common oriented core parameter ; a change of the original core parameter only replaces the unit phase by a smooth unit loop of the same winding number . Let be the unique vertical linear change for which and induce the same normal-quotient identification. Write by smooth polar decomposition, with and positive definite. The compatible-tube assertion [F6] gives an ambient isotopy fixing the core and carrying to near it. The fiber-linear isotopy then connects to through invertible maps. On a common smaller tube its composition with is an isotopy of open embeddings, with open track, fixing the core. The relative open-set clause of [F6] extends it near the compact core. Thus an ambient diffeomorphism , isotopic to the identity through maps fixing the whole link, satisfies near this component. Choose the supports in disjoint component tubes and compose the finitely many isotopies.
Identify with a unit complex number, of winding . The image under of the first chart longitude has slope in the second chart, so preservation of the meridian character gives . The unit loop therefore has even winding. It has a smooth periodic square root : lift its argument on , halve it, and use even winding to match the endpoints and derivatives. In the two branch models the map consequently covers , since . It is an orientation-preserving smooth diffeomorphism including . The two signs of differ by the deck map. Choose the sign matching the complement-cover isomorphism at one point of each connected punctured tube; covering uniqueness makes them agree throughout that tube. Hence the local lifts glue to the complement lift. This proves independence of the oriented smooth total-space diffeomorphism type from arbitrary oriented tubular charts. It does not assert a smooth lift over the identity base map between arbitrary unnormalized charts.
Let be the terminal diffeomorphism of the given ambient isotopy from to . First choose the target tubular charts by transporting the source charts through . Corresponding longitudes have the same character, and in these transported branch coordinates a lift is , or its deck translate. By step 1.2 and [F4] the complement covers are isomorphic over ; on every punctured tube that isomorphism is one of these two local lifts, so it extends smoothly across the branch core. The resulting map is an orientation-preserving diffeomorphism of the closed total spaces. Finally steps 3.1–4.1 compare the transported target charts with any originally chosen target charts. Thus as oriented manifolds, with no unjustified smooth extension of an arbitrary normal germ.
The double branched cover of the trivial two-arc tangle is a solid torus
Statement
Assume the Axiom of Choice. Let be a three-ball and let be the trivial pair of vertical properly embedded arcs, with in the interior of . The connected two-fold cover of whose meridians about both arcs have monodromy extends across as a simple branched cover, and its total space is a solid torus.
Statement references
Facts & Assumptions
Given: AC, the disk with two marked branch points and its product with an interval.
A connected two-fold cover of the punctured disk is determined by the homomorphism that sends each puncture meridian to (Connected covering spaces are classified by conjugacy classes of fundamental-group subgroups).
The simple branching convention is the local square map in an oriented normal disk (Double branched cover of an oriented link). That definition concerns links in ; the disk and product extensions needed here are constructed below.
Euler characteristic is the alternating count of cells in a finite CW structure (Euler characteristic of a finite CW complex); a compact connected boundaryless orientable surface with Euler characteristic is (Classification of compact connected surfaces).
Under AC, two disjoint smoothly embedded circles on cobound an annulus (Two disjoint circles in the two-sphere cobound an annulus).
Proof
Regard as the unit disk in . On the Riemann sphere define , with its usual values at the poles and at infinity. This is a degree-two map branched precisely over : near , and near . The nonzero factors have local square roots, giving exactly the square charts of [F2]. Thus is a compact oriented surface with smooth boundary and a simple branched map to . Its punctured restriction is connected: lifting a meridian about either branch point interchanges the two sheets. By [F1] it is the prescribed disk cover, since the two puncture meridians generate its fundamental group. This constructs the extension rather than assuming it from a link-only definition.
Triangulate the disk with both branch points as vertices. A fan triangulation of an -gon has , , and Euler characteristic ; inserting interior vertices preserves this count. Each open cell lifts twice except the two branch vertices, which lift once. Consequently . The boundary monodromy is , so there are two boundary circles. Capping gives a closed connected orientable surface with Euler characteristic , hence a sphere by [F3]. To apply [F4] with smooth circles in the standard sphere, use the explicit model of step 1.1: the closed exterior disk contains no branch value and is simply connected, so its inverse image consists of two disks by [F1]. Their boundaries are disjoint smooth circles, because is unramified over . Thus is exactly the closed region between these circles in the standard Riemann sphere, and [F4] identifies it as an annulus.
Take . Its local models along the two arcs, including their boundary endpoints, are by step 1.1. Away from the arcs it is the connected product cover with the required meridians. Projection of the punctured product to its disk factor induces an isomorphism on fundamental groups, so [F1] identifies this restriction with the specified cover of . Transporting the constructed extension along that covering isomorphism proves the required extension. Its total space is , a solid torus after the usual rounding of product corners.
Link-surgery filtered complex for a double branched cover
Definition
Let be a finite regular diagram of a nonempty oriented link with ordered crossing set . The resolution cube has vertices , and is obtained by applying the indicated local smoothing at every crossing. The link-surgery filtered module associated to is the direct sum
with the summand for in increasing filtration degree . Choose the subordinate Heegaard multi-diagram, compatible perturbation data and top-generator cycles for successive attaching-curve systems. The diagonal component of the candidate differential is the ordinary hat disk differential. For coordinatewise, sum over every ordered path changing one coordinate at each step. Its summand counts the zero-dimensional holomorphic -gon spaces with input at the vertex, the selected top-generator cycles between each pair of successive attaching systems, and output at the vertex. The count includes the allowed source conformal parameters and imposes zero basepoint multiplicity. These are the surgery polygon maps; the component is zero if . Thus changing several crossings is a sum over paths and polygon counts, not an arbitrary direct edge map. The increasing filtration is , extended by zero below and by at and above . Thus a component increasing lowers its filtration degree and preserves every . The cube direction and the reduced Khovanov cochain degree remain separate indices. The polygon-count finiteness, square-zero, and total-homology identifications are justified by the surgery lemma, which labels its actual Ozsváth–Szabó construction and top-input/filling calculations as external inputs, separately from the retained local analytic theorem and finite filtration algebra.
The local smoothing labels are those of Ozsváth–Szabó Figure1: in the chart with northwest–southeast over-strand, 0 joins the two left and two right endpoints, and 1 joins the two top and two bottom endpoints. These become A and B on the mirror chart, respectively. This fixes the convention for the consumers without a diagram-invariance assertion. The general surgery lemma also applies to links in arbitrary closed connected oriented smooth three-manifolds; this definition is only its branched-cover instance.
Definition references
A two-strand half-twist lifts to an annular Dehn twist
Statement
Let be the positive half-twist mapping class of a disk interchanging two marked branch points and fixed near the disk boundary. Choose its standard supported half-turn representative in coordinates compatible with the local branched square charts, and take its unique smooth lift to the connected two-fold branched cover which fixes the annular boundary pointwise. Its smooth isotopy class relative to that boundary is the positive Dehn twist about the core when the half-twist orientation agrees with the annular orientation, and is the inverse twist when the orientation is reversed. A positive half-twist here is the usual supported rotation through in an oriented disk coordinate containing the two points, interpolated to the identity outside that coordinate disk; the assertion is independent of its cutoff representative.
Statement references
Facts & Assumptions
Given: The disk with two branch points, its connected two-fold simple branched cover, and the supported positive half-twist. All calculations below are finite and use no choice axiom.
Dehn twist on an oriented surface fixes the positive annular formula for the product orientation .
Existence and uniqueness of path lifts through a covering map and Existence and uniqueness of homotopy lifts through a covering map give unique continuation and unique isotopy lifting once one sheet is specified. They apply to the ordinary cover away from the two branch points; the explicit local square coordinate fills those points below.
Proof
An explicit oriented branched annulus. Fix and put , oriented by . Its complex coordinate is , whose complex orientation is this same orientation. The holomorphic map identifies with a two-fold branched cover of the closed ellipse having semiaxes . Its deck map is , and its two fixed points map to . To verify its image and degree, every point outside the real segment lies on a unique confocal ellipse: the expression decreases strictly from a value greater than one to at most one as increases from zero to . Its two preimages have coordinates and . Points inside that segment have the two preimages on , except its endpoints. The derivative vanishes precisely at ; locally and , so each is a simple square branch in smooth complex coordinates. Both boundary components map diffeomorphically to the ellipse boundary.
A commuting twist. Choose a smooth nondecreasing , zero near , one near , equal to on for some , and satisfying . For example choose its upper half from a smooth step and reflect. Set . The symmetry makes modulo , since . It therefore descends to a smooth disk map fixing the ellipse boundary. Near either branch it is , because adds in the central strip, so descent is smooth there as well. In particular interchanges the branch points, and fixes both annular boundaries pointwise. By [F1], is exactly a positive annular twist. It remains to prove the handedness of its quotient, rather than infer it merely from the interchange.
An orientation-preserving disk coordinate. On the quotient of write . Then . Choose and a smooth increasing from to on . Define and there. Extend to so , both derivatives are strictly positive, and both are linear near zero. Here is a finite smooth construction: retain their positive derivative germs near , on an interval so short that each derivative integral is less than half its prescribed value at . Extend each derivative positively and constantly near zero, initially with total integral smaller than that value. Add a nonnegative bump in the intervening interval, with its unique scalar chosen to make the integral equal to that value. Integrating now matches every derivative and the value at . Thus is a smooth odd diffeomorphism from the round disk to . Smoothness and invertibility at zero follow from its positive diagonal linear formula there. Away from zero its Jacobian is . The ellipses are strictly nested, so the equation proves global injectivity and surjectivity. Thus these are actual orientation-preserving disk coordinates, with both branch points inside .
The quotient is the positive half-twist, with its sign. On the central ellipse , and oddness of makes this the polar rotation . On an outer confocal ellipse, changes by , which modulo is the angle . Consequently in the single disk coordinate of step 2.2, where for and outside. This is smooth, one near the branch points, and zero near the boundary. The isotopy replacing the angle by moves the two points counterclockwise through in an orientation-preserving coordinate. Thus it is the standard positive half-twist, not its inverse. This explicitly fixes the relative sign with the positive annular twist in [F1].
Transport to the given cover and lift uniqueness. Apply the preceding model in an oriented coordinate disk supporting the given half-twist. Its branched cover is identified with the model without a covering-classification choice axiom: slit the disk along two disjoint intervals joining the branch points to its outer boundary. Over the resulting simply connected slit disk the two sheets are obtained by unique path lifting from one specified sheet point; endpoints are independent of path by homotopy lifting in [F2]. Crosswise gluing of the two slit banks is forced by the nontrivial monodromy of a small branch meridian, as the local square map shows. This is exactly the gluing of the model. The identifications are smooth locally. At the slit endpoints use the compatible base and source square charts of the chosen representative; the lifted identifications are then linear in the local square-root coordinates and fill smoothly. Outside the support disk its two exterior sheet collars are retained. The two possible lifts differ by ; this deck map interchanges the two boundary components, while fixes them. Thus precisely one lift fixes the annular boundary pointwise, and it is the transported . Only one finite initial sheet choice was made.
Representatives and orientations. Any change of smooth half-twist cutoff is an isotopy through the displayed angle functions, constant near the two points and the outer boundary. Lift it by [F2], using the boundary-fixed sheet. On the complement of the branch points, ordinary smooth local covering coordinates make the lift smooth. Near the branch points the isotopy is the fixed half-turn representative; it therefore extends in the square coordinates and is stationary there. More generally the same argument transports a supplied supported coordinate isotopy defining another standard representative of this half-twist class, chosen standard in the branch charts throughout. It gives a smooth relative-boundary isotopy of lifts. If the annular orientation is reversed, change to while retaining ; the actual formula for becomes . It is the inverse twist in the positively oriented annular convention. Conversely reversing the half-twist motion reverses this angle. These calculations prove the full orientation and standard-representative assertions and also explain why the other, boundary-swapping lift was excluded. The assertion concerns this smooth mapping-class lift; it does not assert that an arbitrary unnormalized smooth base germ has a smooth square-root lift.
The genus-one hat Floer complex of an order-three lens space has rank three
Statement
Assume the ACω hat Floer disk-count theory for closed three-manifolds. For either orientation of , the standard genus-one pointed Heegaard diagram has three intersection generators and its differential over is zero. Consequently has total rank three.
Statement references
Facts & Assumptions
Given: The standard genus-one splitting and the stated filling-orientation convention, and Countable Choice.
In the actual flat torus coordinates the meridians and , , have exactly three intersections, no nonzero normalized periodic domain, no relative disk between different generators, and only the constant relative class at an equal generator. Its proof is the explicit compact-disk lift and affine contraction in the plane, independently of a holomorphic equation. (The straight three-intersection torus diagram has no nonconstant Whitney disks)
The actual allowed hat data have nonnegative region degrees and energy bounded by a fixed positive linear combination of those degrees. Relative homotopies preserve these degrees, since their boundary stays on the attaching circles, away from each region test point. (Nearly symmetric polygons have positive domains and degree energy bounds, Analytic foundations for disk and polygon counts)
The full hat complex and the proved actual move maps identify its homology with the full closed-manifold invariant. The filling convention identifies the unknot-exterior meridian with its preferred longitude , and the attached meridian for with . (Hat Heegaard Floer complex of a closed three-manifold, Hat Heegaard Floer homology is a closed three-manifold invariant, Lens spaces in the filling orientation convention)
Proof
Parametrize the splitting torus by with and . Thus the two compression meridians are and by [F3]. They give exactly the positive-sign diagram in [F1]. Reversing the oriented splitting gives the negative sign diagram; equivalently conjugate the surface coordinate, retaining the same attaching sets. Both signs have three intersections and zero normalized periodic lattice. They therefore satisfy the corrected full-all-sector admissibility condition, including every empty sector; admissibility is not being inferred from a finite set of realized generators.
Take actual allowed generic hat data for either of these literal diagrams. This need not be the flat equation: its prescribed generator charts may be retained. A nonconstant strip would compactify to a relative disk. Distinct endpoints are impossible by [F1]. For equal endpoints the explicit plane contraction of [F1] is a boundary-preserving relative homotopy to the constant map. For each region point q its degree is invariant under this homotopy: the boundary never meets q, so the boundary winding of its small disk, or equivalently the pullback divisor degree, is constant. Every region degree is consequently zero. The ACTUAL positivity and energy inequality in [F2] force zero energy, hence a constant strip. Thus there is no index-one strip for any of these allowed data. At a constant generator its operator is the exact transverse operator of real index zero, as in [F1]; it does not enter the index-one count. This argument does not assume that merely seeing quadrilateral regions excludes arbitrary multiply covered disk domains.
The generator module is therefore with zero differential. Its homology has total rank three. The actual closed-manifold invariance in [F3] identifies this diagram computation with ; the negative-sign calculation proves the same for its reversed orientation. No individual Spin-c grading, absolute normalization or correction term has been inferred from this total rank calculation.
Ozsváth–Szabó link-surgery filtered complex and exact triangle
Statement
Assume the countable-choice Heegaard Floer analytic package. Let be any closed connected oriented smooth three-manifold and let be an ordered framed -component link in . On its th exterior boundary torus let be the meridian and the chosen framing longitude. Use the three filling slopes , and , labelled , respectively; restores the original unfilled component. For let be the simultaneous filling specified by . Fix an admissible pointed Heegaard multi-diagram subordinate to these surgeries and the compatible perturbation and top-generator choices used by the polygon construction. The mod-two polygon maps on form a differential with components only from to coordinatewise. It preserves the increasing filtration extended by zero below zero and by the whole module at and above . Its total homology is isomorphic to . For , the total complex is the mapping cone of the -to- surgery map and is quasi-isomorphic to the hat complex of the third, filling; this yields the long exact surgery sequence for every surgery triad, with its cyclic ordering. For the cube is the single hat complex of . No filtered quasi-isomorphism between distinct surgery presentations is included.
Statement references
Facts & Assumptions
Given: The closed connected oriented smooth three-manifold , the ordered framed link, the filling data , and the compatible admissible multi-diagram and top-generator choices in the Statement.
The general vertex modules and increasing filtration are the ones explicitly specified in the Statement. The branched-cover module is their later special application, rather than a premise restricting this general surgery statement to .
The actual analytic foundations Analytic foundations for disk and polygon counts supply finite zero-basepoint disk and polygon counts, compact one-dimensional boundaries, exhaustive gluing and the resulting identities on the stated operation-specific admissible data: global weak data for all-sector sums, or the prescribed ordinary weak or strict specified-Spin-c families. Positive-rank triples use explicit small triple-free representatives with transported labels; rank zero uses the point model. This supplies neither a subordinate surgery multidiagram nor a calculation that its distinguished top inputs are cycles or satisfy the required higher sums. It does not identify surgery total homology with a filling.
The total homology is interpreted as an invariant of the filled manifold only after closed-manifold Heegaard Floer invariance (Hat Heegaard Floer homology is a closed three-manifold invariant).
External input — actual surgery data and top sums. Ozsváth–Szabó, On the Heegaard Floer homology of branched double-covers, arXiv:math/0309170v1, §4.2, pp.21–23, equation(10) and Lemma4.5: for an ordered framed link in an arbitrary closed oriented three-manifold, the bouquet-subordinate attaching systems use meridians , framing curves , and meridian-added curves , with separately labelled Hamiltonian copies for unchanged systems. On the compatible admissible surgery data the distinguished top inputs are cycles and all monotone top-input sums below vanish. This is the imported operation-specific construction/calculation, not a consequence newly deduced from [F2]. Only its mod-two version is used.
External input — actual single-coordinate surgery cone. The same source, Theorem4.7 and its proof, pp.24–27, equation(12), supplies a quasi-isomorphism between the cone of the two-handle triangle map and the third, meridian filling. Its quadrilateral/top-generator calculation and the cyclic Hamiltonian-copy construction are included in this import; no merely formal null-composition is substituted for that calculation. Its hypotheses are the surgery triad with the subordinate admissible choices above, not an arbitrary pair of chain maps.
External input — total-cube filling comparison. The proof of Theorem4.1, p.27, supplies acyclicity of the enlarged three-valued coordinate complex with its ACTUAL higher polygon entries. It yields the homology comparison with one coordinate filled by , and induction gives the all- filling. Theorem4.1 and Remark4.2, p.17, identify the first differential as the sum of immediate two-handle maps and allow flattening by . This imports the actual total construction; it does not assert guessed canonical coherent comparison maps between arbitrary presentations.
Proof
The cube module and its increasing filtration are fixed by [F1]. The candidate total differential sums over ordered immediate-successor paths and their polygon-count maps, with diagonal disk differential. Each component from to lowers to , so it preserves every increasing filtration subspace whenever the count is defined. Square-zero, count finiteness and identification of total homology still require proof. No filtered comparison between different presentations is a premise of this fixed-data assertion.
The square-zero substitution has a precise additional finite hypothesis. Denote polygon operations by and the chosen immediate top inputs by . For , form the finite top-input sum where every step changes one coordinate; is the differential on a single top input. Suppose the actual surgery data satisfy for every such interval, in their actual auxiliary complexes and compatible labels. Expand the component as the sum over two consecutive input-containing polygon operations. The boundary identity of [F2], summed over all paths from to , pairs these with exactly the terms obtained by inserting one among the top inputs of an input-containing polygon. Every consecutive subpath is counted once in this insertion sum, including length-one differential terms. Thus implies . For this is the vertex differential identity. This is a finite substitution in the actual polygon identities; it does not calculate the top-input sums.
There are only finitely many vertex generators, coordinate paths and required arities. Once the actual admissible subordinate data and top inputs are supplied, [F2] gives finite counts for each term and hence for every differential coefficient. The filtration calculation in step 1.1 then applies literally. In the case, the matrix has diagonal vertex differentials and sole off-diagonal triangle map ; the resulting two-summand complex is its mapping cone with the usual homological shift. This is an actual algebraic identification whenever those data exist, not yet a comparison with the third filling. For it is exactly the given hat complex of .
Apply [F4] to the actual surgery data: its top cycles and vanishing supply exactly the extra hypothesis of step 2.1. Together with the retained local count identities [F2], steps 1.1, 2.1, 3.1 give an actual finite differential preserving the stated filtration. In particular the branched-cover definition later uses a genuine complex, not just a candidate module.
For one coordinate, [F5] supplies the actual comparison of this cone with the third filling, so the cone's short exact sequence gives the surgery long exact sequence. The cyclic triad ordering is the one with slope labels , as fixed in the Statement; the source's Section2, p.6, describes its cyclic symmetry. For zero coordinates the identity complex gives the asserted result.
For several coordinates use [F6], rather than composing unspecified vertexwise comparison maps. Filter the enlarged complex by the first coordinates. Its successive quotients are the acyclic single-coordinate three-term complexes from [F5], including the quadrilateral entry. A finite filtered complex with acyclic successive quotients is acyclic, by induction through the short exact sequences of filtration pieces. The subcomplex with last coordinate and the quotient with last coordinate or therefore have isomorphic homology via the connecting map, with the usual cone shift. Induction identifies the latter cube's total homology with the all- hat homology. The source provides the higher entries of this enlarged complex and their square-zero in [F4], [F5], [F6]; no new canonical comparison map is claimed.
Closed-manifold invariance [F3] identifies this final group with . The construction and every count used here are the imported compatible surgery construction, combined with the retained AComega analytic package. Its geometric data and arities for the fixed link are finite; the cyclic Hamiltonian-copy sequence used in the single-coordinate argument is countable, so the existing countable-choice branch suffices. The source itself does not formulate a choice hierarchy; this accounting uses the retained analytic CC interface and the finite/countable auxiliary selections just specified. No full-AC classification, presentation-independent filtered quasi-isomorphism, or restriction to is introduced.
Unlink resolution covers and the Heegaard Floer TQFT
Statement
Assume the Heegaard Floer analytic package. For every integer , let be a -component planar unlink with an arbitrary orientation on each component, and choose a basepoint on any one component. Its double branched cover is , with . Over , the hat Floer group of this cover is identified with the exterior algebra on a -dimensional vector space, hence has rank . Under these identifications, the cobordism maps for saddle cobordisms between neighboring unlink resolutions, with carried outside the saddle disk, are the multiplication and comultiplication maps of the two-dimensional Frobenius algebra after reduction at the marked component. The identification includes the marked-circle cases and fixes the basis conventions needed to compare the first surgery differential with the reduced Khovanov cube.
Statement references
Facts & Assumptions
Given: The Heegaard Floer analytic package and a planar unlink with , arbitrary component orientations, a basepoint on one component, and the saddle cobordisms between its neighboring resolutions with the basepoint carried outside each saddle disk.
The generic meridian-character construction and local branch convention are recorded in Existence and isotopy invariance of the double branched cover of a link, whose general existence and isotopy-invariance theorem assumes AC. For the planar unlinks here, step 1.1 constructs the required oriented smooth double cover directly by finitely many sheet gluings in the local square-coordinate model. Only that explicit finite realization and local convention are used below; the general AC-dependent existence/classification conclusion is not invoked.
The group is defined by the closed-manifold disk-count complex (Hat Heegaard Floer complex of a closed three-manifold).
The actual analytic foundations Analytic foundations for disk and polygon counts provide finite zero-basepoint disk and polygon counts, compactified boundaries, exhaustive gluing and the resulting identities under their actual operation-specific global weak, ordinary specified-sector weak or strict admissibility hypotheses. They include positive-rank pointed triple-free representatives and the rank-zero point target. These local identities do not compute the exterior-algebra basis or its action, prove a named top input is a cycle, or identify an unlink saddle map with a prescribed Frobenius map.
External input — actual unlink Floer module and handle maps. Ozsváth–Szabó, arXiv:math/0309170v1, Proposition6.1 and proof, pp.32–33: over , is a free rank-one module over , generated by a class . A zero-framed two-handle killing a summand generator induces the exterior quotient, and its dual split operation induces wedge with the new kernel generator. The statement includes the actual triangle-map/-action computation, not merely the dimension of the group.
External input — simultaneously compatible state bases. The same source, Proposition6.2, pp.33–34, including all four cases and Figure11, identifies a based unlink state with this module using lifts of arcs from the marked circle to each other circle , with . Its commutative square(13) identifies EVERY immediate surgery edge in the same state bases. Unmarked merge identifies ; unmarked split has new kernel ; setting gives both marked cases. This is an external input at the chosen finite diagram, not arbitrary unlink naturality or a new locally proved count.
Proof
The topology assertion has a direct finite construction. Put the planar -component unlink, , in its standard -bridge position: the upper and lower balls each contain boundary-parallel arcs with the same noncrossing matching of their endpoints. Choose their disjoint bridge disks. Cutting either ball along those disks trivializes the branch construction. Its double cover is two balls joined by one-handles; the first joins the two zero-handles, and each remaining handle adds one genus. Thus it is a genus- handlebody. The two bridge matchings and disk systems agree in the projection sphere, so the cover of the unlink is the double of this handlebody with matching meridian disks. Doubling each of its co-core disks gives disjoint nonseparating two-spheres. Cutting them removes those one-handles and leaves a sphere with paired ball holes; regluing the pairs gives . For it is the double of a ball, hence . The cover is constructed by crosswise gluing two labeled copies of the cut balls along the finitely many bridge disks, using along the branch arcs and the matching endpoint charts. These charts give its orientation and smooth structure directly. Thus this is a finite realization of the local branch convention in [F1], without invoking the generic AC-dependent covering classification or any Floer map.
Here is the complete finite algebra to which the external Floer map computation [F4]–[F5], applied below is applied. Order the unmarked circles of a based -circle state, and assign to them generators . The reduced state space is : the basis monomial on a subset labels those circles by , the others by , and the marked circle by the quotient label . Exterior multiplication is commutative over and each . Thus this state space has dimension , once an actual Floer vertex identification with it is supplied. This is a computation of the required state algebra, not yet of .
Write . For an unmarked merge the required map is , , . For an unmarked split it is , . If a marked circle merges with an unmarked one, reducing the output kills on the marked factor, so and . If a marked circle splits, reduce the child containing the original point: then becomes (with factors exchanged when necessary). Hence marked split creates the unmarked label , not . All untouched factors are carried identically. These are literal quotient calculations and include both marked cases.
Equivalently, unmarked merge is the exterior-algebra quotient identifying with . Unmarked split is , where and other generators are unchanged; choosing instead gives the same map, since . Marked merge is quotient by the disappearing , and marked split is wedge with the newly created . Thus these four precise quotient/wedge operations, in a common state basis, are the finite map targets for the analytic surgery-edge calculation.
Apply [F4] to the actual cover constructed in step1.1. Its rank-one exterior module gives the rank , with generators represented by the arc lifts specified in [F5]. That same input supplies the actual Floer triangle maps and their common state bases. Under these bases the quotient/wedge operations of [F4], [F5] are precisely the four finite reduced tables proved in steps 1.2, 2.1, 3.1. In particular kills the unwanted marked-circle factor and forces marked split to create the new label.
The vertex and map computations in the preceding step are externally imported, not inferred from analytic regularity [F3] or from a chosen common-top transfer. The topology and quotient algebra remain the local finite arguments above. All coefficients are , so no integral sign or instanton-saddle formula is used. The actual finite diagram has finitely many states and edges, with the analytic data in the stated AComega branch. This proves the full fixed-resolution Floer TQFT assertion with its compatible marked bases.
The trefoil double branched cover is a lens space of order three
Statement
Assume the Axiom of Choice. Let be either oriented trefoil in . Its double branched cover is diffeomorphic, up to orientation reversal, to the lens space in the convention in which is the filling of the standard unknot exterior. In particular, is cyclic of order three.
Statement references
Facts & Assumptions
Given: AC and the closure of the two-strand braid , or , with the given knot orientation; the cover conventions of the statement. Circle coordinates below are taken modulo , and the page parameter modulo one.
Double branched cover of an oriented link and Existence and isotopy invariance of the double branched cover of a link give the meridian-character cover and its simple branched extension, and invariance under the chosen oriented link isotopies.
The double branched cover of the trivial two-arc tangle is a solid torus supplies the annular cover of the disk with two branch points and its product extension over an interval.
A two-strand half-twist lifts to an annular Dehn twist gives the unique boundary-fixed smooth mapping-class lift of a positive half-twist as the positive annular twist, with the inverse for its reverse. It includes the actual orientation/sign calculation.
Lens spaces in the filling orientation convention defines as the unknot-exterior filling with meridian slope .
Seifert–van Kampen identifies the fundamental group with a group pushout identifies the fundamental group of a two-solid-torus union as the pushout of its boundary inclusion maps. Thickening the two pieces by collars gives its required open connected cover.
Proof
The covered disk pages and their binding fillings. Use the standard disk open book of about the braid axis : its complement of a small axis neighborhood is , and the closed two-strand braid meets each disk in two points. This description is explicit in : the axis is and the page parameter is ; the disk page is parametrized by , with having the remaining modulus and chosen argument. Cut the page parameter at zero. The two moving points over the resulting interval are a braid isotopy of the twice-marked disk. Its double branched cover is the corresponding annular product by the same square-coordinate and sheet-gluing construction as [F2]. On gluing the ends, the annular monodromy is the boundary-fixed lift of the braid mapping class, hence by [F3]. There is no extra deck map: the page-parameter loop near the axis bounds a small meridian disk in its neighborhood disjoint from the branch link, and has trivial meridian character. Moreover the axis itself links the two-strand braid twice, so its mod-two character is zero as well. Thus the cover of its solid-torus neighborhood consists of two ordinary copies, one for each annular boundary. In each copy the meridian is the loop at a fixed boundary-page point. Consequently the whole branched cover is exactly the annular mapping torus with both boundary tori filled along these page-parameter meridians. The local branched models retain the smooth structures.
Untwist the mapping torus, retaining both meridians. Write , with a positive twist , where near and near . The mapping torus has the equivalence . The function is well-defined across that equivalence and gives an actual diffeomorphism of the mapping torus with . Its inverse on the cut parameter interval is , with the same endpoint compatibility. At the lower boundary the filling meridian has class in the basis. At the upper boundary the corresponding meridian has class . This computes their actual slopes, not only their intersection number.
The two solid tori. Split the product at any fixed interior . Fill its lower end along . This caps the circle in the annulus by a disk, so that piece is the solid torus . Its meridian on the common torus is and its core longitude is . The upper filled piece is also a solid torus: the integral shear extends over its whole product collar, is single-valued because is an integer, and takes its filling slope to . After that shear it is the same disk-capped product as the lower piece. Before undoing the shear, its meridian on the common torus is precisely . Hence this is a genus-one gluing with that meridian slope.
Identify the fixed unknot peripheral basis. Identify with the standard unknot exterior, using the same decomposition: for a small standard axis neighborhood . On its boundary the unknot meridian is the circle, which generates the core circle of , and the preferred longitude is the circle, which bounds its meridian disk. Thus take , by an actual product-coordinate identification. Up to the global orientation choice allowed in the statement, the other solid torus is attached with meridian . For this is exactly [F4]. For , the reflection reverses the orientation of , preserves the unknot, and sends to and to . It carries the slope to and extends over the filled solid torus by the same meridian identification. Hence the other handedness has the same description up to orientation reversal. Reversing the orientation of the branch knot does not change its mod-two meridian character.
In the group is generated by and is trivial, by its product coordinates. Gluing the second solid torus kills the slope . By [F5] there are no further relations: a primitive complementary boundary longitude identifies the core generator of the attached solid torus with the corresponding word in the exterior generator, so that generator is eliminated from the pushout presentation. The group is therefore , cyclic of order . All new coordinate and slope calculations were finite; the only inherited choice use is the already declared cover and peripheral-convention branch. This proves both assertions for either oriented trefoil without replacing a meridian-slope calculation by the determinant alone.
Reduced Khovanov cohomology of a based link over F2
Definition
Let be a finite regular oriented link diagram with a marked point away from crossings, and let be its normalized Khovanov cochain complex over obtained from the algebra with and . On each resolution state, let multiply by on the circle containing and act as the identity on the other circle factors. Define the reduced complex by , with the surviving based-circle label assigned reduced quantum degree by the shift . Its cohomology is . The basepoint may lie on any component; for a link, independence of the chosen component is a separate theorem.
Definition references
Normalized Khovanov cube and edge signs
The Frobenius algebra and merge/split maps
Square-zero of the unreduced cube differential
Integral based-knot reduction convention
Ozsváth and Szabó, On the Heegaard Floer homology of branched double-covers, §5
Facts & Assumptions
Given: A finite regular oriented link diagram and its normalized Khovanov cube over .
The circle algebra is , with multiplication and comultiplication , (Khovanov Frobenius algebra and cube of resolutions).
Every cube edge is the corresponding merge map or split map , tensored with identities on unaffected circles (Khovanov chain complex from a diagram).
The signed Khovanov differential squares to zero over the integral algebra, and hence its reduction modulo two also squares to zero (The Khovanov cube differential squares to zero).
Each diagram produces a finite normalized cochain complex (The Khovanov diagram procedure terminates and returns a finite cochain complex).
Proof
If an edge avoids the marked circle, its map acts as the identity on that factor and commutes with . For a merge involving the marked circle, associativity gives , with the marked factor placed on the appropriate input. For a split of that circle, the Frobenius identity gives ; for both sides equal , and for both sides vanish. Thus every edge map commutes with , so is a subcomplex.
The quotient differential is well-defined by step 1.1 and squares to zero by [F3]. In each state the marked-circle factor has basis , and multiplication by has image the one-dimensional span of . The quotient therefore replaces that factor by ; the shift assigns the surviving label degree zero. This gives the stated reduced cochain complex and its cohomology.
The first surgery differential is the reduced Khovanov TQFT differential
Statement
Assume the Heegaard Floer analytic package. Fix a finite regular diagram of a nonempty oriented link , choose a basepoint away from the crossings, and choose an admissible pointed Heegaard multi-diagram subordinate to the branched-cover surgeries, with the compatible perturbation data and top-generator cycles of the link-surgery construction. Identify each first-page vertex group with the reduced state space of the corresponding crossingless resolution, based at the circle containing . For every cube edge, the induced first differential is the mod-two map assigned by the saddle: multiplication when two resolution circles merge and comultiplication when one resolution circle splits, with the marked-circle quotient at . Under these identifications the direct sum of edge maps is the reduced Khovanov differential of the mirror diagram , based at the corresponding point, in the Ozsváth–Szabó smoothing convention.
Statement references
Facts & Assumptions
Given: The Heegaard Floer analytic package and a fixed finite regular diagram of a nonempty oriented link , a basepoint on the diagram away from the crossings, its surgery cube, and the mod-two Heegaard Floer groups and edge maps for every crossingless resolution.
The surgery complex has the vertex groups and edge filtration described in Ozsváth–Szabó link-surgery filtered complex and exact triangle.
The unlink vertex groups and all marked/unmarked saddle maps are identified, in simultaneous state bases, as the reduced Frobenius TQFT (Unlink resolution covers and the Heegaard Floer TQFT).
The reduced Khovanov complex uses precisely the marked-circle quotient and merge/split maps in Reduced Khovanov cohomology of a based link over F2.
External input — local surgery/mirror smoothing identification. Ozsváth–Szabó, arXiv:math/0309170v1, Section2 Proposition2.1 and following paragraph, pp.6–7, together with Figure1 p.2 and Theorem6.3 pp.34–35, identifies the three branched fillings with crossing/0/1 resolutions and the immediate surgery edge with the saddle. In its displayed chart the over-strand is northwest–southeast, the 0-resolution joins the left pair and the right pair, and the 1-resolution joins the top pair and bottom pair. After switching over/under to form the mirror, this is exactly A then B in the library source chart. Thus the surgery bits agree with the mirror Khovanov 0/1 bits. Only the fixed-diagram mod-two assertion is imported.
Proof
On the associated graded cube the diagonal differential is the ordinary vertex differential. Therefore its homology is the direct sum of the resolution Floer groups. The next differential is induced by the components changing one coordinate: higher polygon components lower the increasing filtration by at least two and cannot contribute to this first differential. Each surviving component is the actual surgery triangle map of that edge.
Use the SAME vertex state identification simultaneously for all incident edges. By the exact Floer supplier [F2], an unmarked merge has table , , ; an unmarked split has and . Marked merge kills the input with the other circle labelled and sends its input to . Marked split sends to , with the tensor order determined by which child contains the point. These last two formulas are obtained by quotienting the marked factor, not by keeping an extra unreduced factor. Tensor the identity on every untouched circle. These are exactly the reduced Frobenius saddle maps of [F3].
For an explicit grading binding, let be the signed crossing counts. By [F4] the surgery bit vector is the vector of , so the normalized cochain degrees are where , with degrees , and the marked surviving label has reduced degree zero. Every saddle table in step 2.1 lowers the sum of label degrees by one, including marked merge and split. Increasing by one therefore raises by one and preserves . The spectral-sequence filtration index satisfies ; it is not an independent Floer cochain grading.
The finite direct sum of the simultaneously compatible vertex identifications in [F2] is consequently an isomorphism with the normalized reduced Khovanov cube of the mirror. The actual surgery-to-mirror chart correspondence is [F4]; the grading shifts follow independently from the library cochain definition in step 3.1, rather than from an unconverted homological index in the source. No arbitrary separate edgewise changes of basis are used. This proves the direct-sum first-differential assertion for the fixed diagram, without a diagram-independence claim.
Reduced Khovanov homology over F2 is independent of the chosen link component
Statement
Let be a finite regular diagram of an oriented link and let be any two points of away from crossings, possibly on different link components. Over , the reduced Khovanov cohomology groups defined using and are isomorphic as bigraded vector spaces. The isomorphism need not be canonical; no diagram-change invariance is asserted here.
Statement references
Facts & Assumptions
Given: The finite Khovanov cube and two basepoints away from its crossings.
The circle algebra and all edge maps are the Frobenius multiplication and comultiplication specified in Khovanov Frobenius algebra and cube of resolutions and Khovanov chain complex from a diagram.
The cube is a finite cochain complex with (The Khovanov cube differential squares to zero, The Khovanov diagram procedure terminates and returns a finite cochain complex).
The based reduced complex is the quotient by with the stated one-degree shift (Reduced Khovanov cohomology of a based link over F2).
Proof
On define and , and on a state tensor define as the sum of this operation over its circle factors. For multiplication, direct evaluation on gives . For comultiplication, evaluation at gives , and evaluation at gives . Thus commutes with each saddle map and hence with . Also : applying twice to one circle gives zero, and every pair of distinct circles occurs twice, hence cancels over .
For a basepoint , multiplication is a chain map and . The local operators on the circle containing satisfy on that factor; terms of on all other circles commute with and occur twice in the sum, so the identity holds on every state tensor.
Put and . The identity in step 2.1 and imply , , , and . Both maps commute with by step 1.1. Moreover : one inclusion follows from , and gives the reverse inclusion. Hence the chain module splits as .
The quotient map identifies with . The restriction is an isomorphism with inverse , since is the identity on and is the identity on . The map lowers raw quantum degree by two, while [F3] lowers the quotient grading by one. Thus, for each cohomological degree , if is the dimension of unreduced cohomology in raw degree and the dimension of reduced cohomology in reduced degree , then .
The diagram has finitely many cube generators, so the sequences and have finite support. Rewrite step 4.1 as . For each parity of , start above the largest supported reduced degree, where the latter term is zero, and recurse downward by two; this uniquely determines all reduced dimensions from the unreduced dimensions. Therefore in every bidegree. Finite-dimensional vector spaces with equal dimensions are isomorphic in each bidegree; only finitely many bidegrees occur, so these isomorphisms assemble without an infinite choice principle.
The reduced Khovanov homology of a trefoil has rank three
Statement
Let be the oriented closure of the two-strand braid , with both strands directed downward and the positive generator drawn with its southwest-to-northeast strand over its northwest-to-southeast strand. Mark a point away from the three crossings, use the A-smoothing (zero-resolution) as the through pairing, and use the B-smoothing (one-resolution) as the cap-cup pairing. The normalized reduced Khovanov cohomology of over has total rank . The normalized cohomological and quantum grading shifts do not change this total rank.
Statement references
Facts & Assumptions
Given: The three-crossing two-strand braid closure, a basepoint, and its reduced cube over .
The based reduced state space removes the marked-circle factor, and a split of that circle maps its surviving label to on the unmarked output. The supplier proof verifies that the marked action commutes with every edge map, so the quotient is a cochain complex (Reduced Khovanov cohomology of a based link over F2).
The circle algebra has , multiplication , and comultiplication , (Khovanov Frobenius algebra and cube of resolutions).
The signed Khovanov differential squares to zero, and the finite diagram procedure outputs a finite cochain complex (The Khovanov cube differential squares to zero, The Khovanov diagram procedure terminates and returns a finite cochain complex).
The diagram procedure enumerates all smoothing states and assigns the merge or split edge map at each crossing change (Khovanov chain complex from a diagram).
Proof
Let be the number of one-resolutions. The all-through closure has two circles; for , the first cap-cup gives one circle and each additional cap-cup contributes one closed circle. Thus the eight state circle counts in lexicographic order are . Removing the marked circle gives reduced state dimensions , so the cube cochain dimensions are .
Order states within each cohomological degree lexicographically and order free circle factors by their first encounter in a fixed diagram scan, with before . The quotient by the marked-circle action in [F1], the Frobenius maps in [F2], and the edge procedure in [F4] give , , and . In each merge sends and . In each target gets two marked-circle splits . For , on target basis the three source-state maps are , , and . These are exactly the marked quotient split maps and the ordinary Frobenius split map, in the stated basis order.
The matrix has rank . In , the first two columns are independent and their sum is the third, so . The last matrix has three independent nonzero rows, so . By [F1] the quotient is a cochain complex, and [F3] gives its finite support; hence its cohomology dimensions are , , , and . The total rank is therefore , and grading shifts preserve total dimension.
The E1 differential of the link-surgery complex is reduced Khovanov
Statement
Assume AC and the ACω Heegaard Floer analytic package. For a fixed finite regular diagram of a nonempty oriented link , with crossings and a basepoint away from the crossings, choose an admissible pointed Heegaard multi-diagram subordinate to the branched-cover surgeries and the compatible perturbation data and top-generator cycles of the link-surgery construction. Its first page and first differential are isomorphic as a cochain complex over to the reduced Khovanov cochain complex of the mirror diagram , based at the corresponding point, in the specified normalized grading shifts. The resulting second page is therefore the based reduced Khovanov cohomology of . The isomorphism is for this fixed diagram and makes no claim about filtered chain complexes for different diagrams.
Statement references
Facts & Assumptions
Given: AC, the ACω Heegaard Floer analytic package, a fixed finite regular diagram of a nonempty oriented link , its filtered surgery complex, and a marked point away from the crossings.
The filtration's first differential is the sum of the cube-edge maps (The first surgery differential is the reduced Khovanov TQFT differential).
The first surgery differential is the reduced Khovanov TQFT differential supplies simultaneous vertex identifications intertwining every saddle edge with the reduced Frobenius map, including the marked-circle quotient, and identifies the surgery bits with the mirror smoothing bits. The target quotient and normalized grading convention are those of Reduced Khovanov cohomology of a based link over F2; the shifts below are calculated from that convention, not asserted as an extra clause of the supplier's Statement.
Over , the isomorphism class of the reduced cohomology does not depend on the marked component, for a fixed diagram (Reduced Khovanov homology over F2 is independent of the chosen link component).
Proof
The filtration quotient at each cube vertex is its resolution Floer group, and the differential on the first page is the sum of components changing one crossing.
Applying the asserted edge identifications [F2] to each of the finitely many edges identifies this first-page differential with the reduced Khovanov cube differential; the finite direct sum of the vertex isomorphisms is an isomorphism of cochain complexes.
Write and let label the unmarked circles of a state , with quantum degrees . Mirroring interchanges and , so the normalized target convention in [F2] gives and . The marked quotient label has reduced degree zero. Unmarked saddles lower the label-degree sum by one. A marked merge sends the other circle's to the marked and kills its ; a marked split creates on the new unmarked circle. Their nonzero terms also lower the unmarked degree sum by one. Thus every edge raises by one and preserves . These degrees are transported from the reduced state bases to ; no independent Floer quantum grading is asserted. For filtration index the cochain reindexing is .
Taking cohomology of the identified first-page complexes gives the based reduced Khovanov cohomology on the second page, with the shifts checked in step 3.1. By [F3] its graded isomorphism class is independent of the chosen link component for this fixed diagram. The actual Floer saddle and mirror identifications are the supplier inputs in [F2]; the finite assembly and normalization above introduce no further geometric assertion. This proves the stated identification and asserts no map between distinct diagram presentations.
Reduced Khovanov homology over F2 is an oriented link invariant
Statement
Assume ACω. For every nonempty oriented link , the bigraded vector spaces obtained by reducing the normalized Khovanov complex at a point on any chosen component are independent, up to noncanonical bigraded isomorphism, of the diagram and the chosen component. No filtered structure from a Floer construction is part of this invariance statement.
Statement references
Facts & Assumptions
Given: ACω, two finite regular diagrams of the same nonempty oriented link, and a basepoint on a component of each diagram.
Every nonempty oriented link in has a finite regular diagram: move it off using the link definition's ambient-isotopy convention, then choose a regular projection direction. Since the crossing set is finite, each component has points away from crossings at which it can be based (Oriented links in the three-sphere and ambient isotopy, Existence of regular projections).
Under ACω, two diagrams of the same oriented link are connected by a finite sequence of planar isotopies and oriented Reidemeister moves (Reidemeister's theorem for oriented diagrams).
For every oriented link Reidemeister move with an unchanged exterior mark, the actual normalized integral maps and inverse homotopies commute with the marked actions and descend to bigraded equivalences of the quotient complexes; reducing the same identities modulo two proves the corresponding based-link equivalences over (Based-link reduced Khovanov equivalences for every local Reidemeister move).
For a fixed diagram, the reduced cohomology is independent of which link component carries the basepoint (Reduced Khovanov homology over F2 is independent of the chosen link component).
The based reduction is the quotient by the image of the basepoint action (Reduced Khovanov cohomology of a based link over F2).
Proof
By [F0], the based reduced groups in the Statement are defined for diagrams of every nonempty oriented link. For any two such diagrams , [F1] gives a finite sequence of planar isotopies and oriented Reidemeister moves. For a Reidemeister step choose a marked point on an unchanged exterior arc and carry it to the corresponding arc on the other diagram. Such an arc exists: the move models contain a continuing strand meeting the boundary of their disk, and a closed regular link diagram continues that strand outside the disk. For a planar isotopy choose any mark and carry it by the isotopy. There are finitely many steps and every diagram is nonempty, so these are finite point choices, adding no choice hypothesis beyond [F1]. These auxiliary marks need not all lie on a single tracked component.
At the start of a step, [F3] identifies the current reduced group with the reduction at its chosen auxiliary mark, even if that mark lies on another component. For a Reidemeister move, [F2] then gives a bigraded cochain homotopy equivalence between the reductions at the two unchanged exterior marks. Its integral maps and contractions commute with the marked action before quotienting, and their explicit equations remain true over . For a planar isotopy the relabeling of circles preserves that marked factor and every normalized degree. Thus each step supplies a bigraded cohomology isomorphism, followed if necessary by another fixed-diagram change of mark using [F3].
Compose these finitely many isomorphisms, using [F3] at the first and last diagram to reach the originally selected marks. This proves independence of the diagram and chosen component. For an empty move sequence only [F3] is needed. Each vector space has finite support in its bigrading, so finite choices of its isomorphisms assemble the asserted noncanonical bigraded isomorphism. The proof uses neither a canonical identification of different move sequences nor a relative movie theorem for multi-component cut tangles. ACω is used only in [F1]; the local tensor equations and fixed-diagram mark changes are finite and choice-free.
The Ozsváth–Szabó spectral sequence for a fixed link diagram
Statement
Assume AC and the ACω Heegaard Floer analytic package. Let be any finite regular diagram of a nonempty oriented link , with a marked point away from crossings. There is a spectral sequence over associated to the link-surgery filtered complex for this fixed diagram whose page is isomorphic, with the normalized grading shifts of the chosen smoothing convention, to computed from the mirror diagram, and whose abutment is with its image filtration. This is a fixed-diagram construction; it does not assert a diagram-independent filtered quasi-isomorphism type.
Statement references
Facts & Assumptions
Given: AC, a nonempty oriented link diagram with a basepoint, and the stated ACω Floer disk and polygon theory.
The diagram determines the surgery cube of branched covers and its filtration (Link-surgery filtered complex for a double branched cover).
The surgery cube is a filtered chain complex with total homology identified with the hat Floer homology of the branched cover (Ozsváth–Szabó link-surgery filtered complex and exact triangle, Hat Heegaard Floer homology is a closed three-manifold invariant).
The first page and its differential identify with the reduced Khovanov cube of the mirror diagram (The E1 differential of the link-surgery complex is reduced Khovanov).
A finite filtration yields a convergent spectral sequence to the associated graded of the filtered homology (Filtered convergence and the scope of the Ozsváth–Szabó construction).
Proof
The crossing resolutions of give the vertices of the cube, and the surgery maps give the differential components. By [F2] these components square to zero and preserve the increasing cube filtration, so the associated spectral sequence is defined.
The filtration has only the levels , where is the number of crossings. By [F4] the spectral sequence stabilizes and abuts to the image filtration on the total homology, which [F2] identifies with .
The associated graded vertex groups form the page, and their first differential is the sum of the single-crossing edge maps. By [F3], this complex is isomorphic to the reduced Khovanov complex of the mirror diagram; taking its cohomology gives the stated page.
The proof used one fixed and the finite filtration only. It supplies no filtered map between the constructions for two diagrams, so it establishes the stated fixed-diagram spectral sequence but no diagram-independent filtered quasi-isomorphism. Here [F2] uses the explicitly external OS surgery construction and filling comparison, and [F3] uses its actual compatible unlink maps with the proved finite reduced-algebra binding. Those imports retain their stated scope; no missing geometric map is inferred from finite convergence.
The Khovanov to branched-cover Heegaard Floer spectral sequence
Statement
Assume AC and ACω. For every nonempty oriented link , there is a spectral sequence over whose page is the reduced Khovanov cohomology of the mirror link and whose abutment is with its image filtration. The page identification is an isomorphism of bigraded vector spaces; this statement does not claim a diagram-independent filtered quasi-isomorphism type for the chain-level spectral sequence.
Statement references
Facts & Assumptions
Given: AC, ACω, and a nonempty oriented link .
Every nonempty oriented link in has a finite regular diagram: move it off using the link definition's ambient-isotopy convention, then choose a regular projection direction. Every component has a point away from the finite crossing set for the basepoint (Oriented links in the three-sphere and ambient isotopy, Existence of regular projections).
The branched cover is well-defined up to oriented diffeomorphism (Existence and isotopy invariance of the double branched cover of a link).
For a fixed diagram, the surgery construction has equal to based reduced Khovanov cohomology and converges to the branched-cover Floer group (The Ozsváth–Szabó spectral sequence for a fixed link diagram).
Over ACω, the reduced Khovanov group is independent of the chosen diagram and marked component up to bigraded isomorphism (Reduced Khovanov homology over F2 is an oriented link invariant).
AC is used by the link-complement and covering-space construction; ACω is separately used by the Reidemeister-move and generic Floer analytic branches (The Axiom of Choice, The Axiom of Countable Choice ()).
Proof
By [F0], choose an ambient-isotopic representative with a finite regular diagram and a point on its mirror away from crossings. Apply [F2] to ; this gives a spectral sequence with equal to the based reduced Khovanov group of the mirror diagram and abutment . By [F1], .
Apply [F3] to identify that page, up to bigraded isomorphism, with independently of the selected diagram and component. The convergence in [F2] and target invariance in [F1] give the stated invariant endpoints, with no diagram-independent filtered chain claim.
The two deductions above are exactly the stated endpoint construction relative to [F2] and [F3]. They preserve the fixed-diagram scope of the filtered construction and use only the invariant isomorphism classes of its endpoints. Thus the formal assembly is complete relative to these two exact supplier interfaces.
External-input boundary
The fixed-diagram supplier uses the explicitly labelled external Ozsváth–Szabó surgery and unlink-map inputs, with exact locators and reading limits recorded in those suppliers and the run source receipt. The reduced link-invariance supplier supplies the independent based-link passage. This proof assembles those results; it does not reconstruct their imported parts or claim a diagram-independent filtered chain type. AC for the branched cover and ACω for the analytic/Reidemeister branches remain the separate assumptions of the Statement.
4 · Examples, counterexamples and false statements
None yet.
Sources
- Ozsváth and Szabó, On the Heegaard Floer homology of branched double-covers, §§1–2
- Hatcher, Algebraic Topology, Theorem 1.38 and Proposition 1.39
- Ozsváth and Szabó, On the Heegaard Floer homology of branched double-covers, §1.1 Further remarks and speculation, printed pp. 3–4; filtered quasi-isomorphism discussion on p. 4
- Weibel, An Introduction to Homological Algebra, Chapter 5
- Lipshitz, Heegaard Floer Homologies, §5
- Ozsváth and Szabó, On the Heegaard Floer homology of branched double-covers, §2, Proposition 2.1
- Hatcher, Algebraic Topology, §3.3 and Theorem 1.38
- Ozsváth and Szabó, On the Heegaard Floer homology of branched double-covers, §2, proof of Proposition 3.1
- Ozsváth and Szabó, On the Heegaard Floer homology of branched double-covers, §§2 and 4
- Ozsváth and Szabó, On the Heegaard Floer homology of branched double-covers, §2, Figure 2
- Ozsváth and Szabó, On the Heegaard Floer homology of branched double-covers, §3
- Ozsváth and Szabó, Holomorphic disks and topological invariants for closed three-manifolds, §§3–4
- Lipshitz, Heegaard Floer Homologies, §§2–5
- Ozsváth and Szabó, On the Heegaard Floer homology of branched double-covers, §§2 and 4, Theorems 4.1 and 4.7
- Ozsváth and Szabó, On the Heegaard Floer homology of branched double-covers, Propositions 6.1 and 6.2
- Ozsváth and Szabó, On the Heegaard Floer homology of branched double-covers, §5
- Shumakovitch, Torsion of the Khovanov homology, §2.2
- Turner, A hitchhiker’s guide to Khovanov homology, §1.2
- Ozsváth and Szabó, On the Heegaard Floer homology of branched double-covers, §6, Propositions 6.1–6.2
- Lipshitz, Heegaard Floer Homologies, §5.3
- Shumakovitch, Torsion of the Khovanov homology, §§3.1–3.2
- Ozsváth and Szabó, On the Heegaard Floer homology of branched double-covers, §6
- Ozsváth and Szabó, On the Heegaard Floer homology of branched double-covers, Theorem 6.3 and proof
- Shumakovitch, Torsion of the Khovanov homology, §§2.2 and 3
- Ozsváth and Szabó, On the Heegaard Floer homology of branched double-covers, Theorem 1.1, Corollary 1.2, and §6