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Satellite operators preserve concordance
Statement
Let P⊂S¹×D² be a smooth oriented pattern. If oriented knots K₀ and K₁ are concordant in one of the four categories C_sm, C_top, C_ex or C^{1/n}, then P(K₀) and P(K₁) are concordant in the same category. Thus P induces a well-defined set map on each of these concordance sets.
Statement references
Facts & Assumptions
Given: A pattern P and a concordance annulus A from K₀ to K₁ in one of the stated ambient categories.
Satellite insertion uses a zero-framed tubular copy of S¹×D² around each endpoint knot (Satellite operators on concordance classes).
Each category specifies the ambient 4-manifold and regularity of its concordance annulus (Exotic and localized homology concordance classes).
External TOP input (not reconstructed here). A locally flat proper surface in a topological four-manifold has an actual rank-two normal VECTOR-bundle neighborhood; where such a neighborhood is prescribed near a closed subset, including the boundary collars, it can be chosen to agree with that germ on a smaller neighborhood. This is Freedman–Quinn Theorem9.3A, printed137–141, used under the run-specific external-source boundary. It supplies the actual tube, not automatic agreement of arbitrary global framings. The cited statement and proof pages137–141 were read; no full-book reading or local reconstruction is claimed.
Every ambient concordance manifold here is oriented and is an -homology , with in the standard, TOP and exotic cases and in the localized case. This follows from the defining ambient conditions. Exotic and localized homology concordance classes
Compact finite-input convention. The classical external results are initially used in ordinary ZFC, not assumed choice-free from their citations. For this one application take finitely many charts covering the given compact manifolds and finitely many pair charts covering each given compact disk or annulus, shrinking to closed inner charts inside open outer charts. Such finite subcovers exist by compactness; selecting this finite list uses no axiom of choice. Include the actual boundary/product collars and all supplied homeomorphisms in the list. Encode chart domains and overlaps by their rational balls, continuous maps and their inverses by dense rational data with moduli on the closed inner charts, and smooth maps by all finite-order derivative and Taylor-remainder data. The modulus at each integer scale is the least integer satisfying its uniform-continuity bound; restrictions to rational compact boxes use the least box index. These are uniquely defined choices from subsets of , not a countable family of freely selected charts. Include positive open-image and overlap margins, inverse identities, finite cover/Lebesgue bounds, and the pair-section identities with positive separation from the compact outside-patch remainder. On the standard disk/annulus parameters the latter certify the actual plane section, not merely a continuous embedding. One real codes these finitely many maps and their canonical countable data. The external relative-constructibility input is that is an inner model of ZFC containing (Karagila, §8.3, p.42); no ambient choice hypothesis is required. All compact maps are decoded using these same moduli, so the inverse identities, covers, pair sections and collar equalities are checked on dense rational sets with their displayed buffers and remain valid in the ambient universe . An internally produced compact witness is exported with the same certificates, and hence is an actual ambient compact witness. This uses the peer-checked compact annulus coding pattern of the standard connected-sum compatibility supplier only at its geometric scope; it does not assert that arbitrary homology or fundamental-group hypotheses are absolute.
Proof
For the TOP annulus the ambient manifold is the standard compact product, and the given annulus and end collars have exactly the finite pair-code description in [F5]. Apply the external normal theorem [F3] inside with those collars. Restrict the resulting tube to a compact disk bundle, still with a slightly wider domain, and export its forward/inverse, pair and collar certificates as in [F5]. This gives an actual relative tube in without ambient AC. For the smooth annuli in the other three categories, a finite chart partition of unity gives a metric and connection along the compact annulus; parallel transport and the compact inverse-function construction give the smooth tube. Only finitely many chart choices and least integer radii are needed. Thus the external TOP input used below is earned at this particular finite input; no global choice-free version of FQ is being asserted.
In the smooth product category, choose a tubular neighborhood of the smooth annulus A. Its oriented normal 2-plane bundle over A has relative Euler obstruction in H²(A,∂A;Z)≅Z. The boundary trivializations are the zero framings of K₀ and K₁; the relative obstruction is the difference of their self-linking numbers, hence zero. A relative framing therefore identifies a neighborhood of A with A×D² and agrees with the two prescribed endpoint zero-framed neighborhoods.
In that framed neighborhood insert in every disk fiber. Orient the inserted annulus by the interval direction followed by the pattern orientation. Its oriented boundary is then at the lower end and at the upper end. The product collars of and the endpoint framings give product collars matching the ambient end collars, and the two endpoint patterns use the preferred zero framings. This proves concordance preservation for smooth annuli in a standard product.
In the exotic and localized cases the annulus is smooth, so the same smooth tubular construction is available in its given smooth ambient manifold. In the TOP case use the external input [F3] relative to the two actual smooth endpoint collars. In every case this gives an oriented rank-two vector normal bundle over . Its obstruction to a framing extending the two preferred zero framings is its relative Euler number in . Cap by boundary Seifert chains with opposite boundary orientations and push the caps into the product collars. Their union is a closed two-cycle. Its intersection with a relative small parallel copy of is the relative Euler number, because the two cap terms are precisely the endpoint zero-linking numbers. The cycle is zero over by [F4], so that Euler number is zero in . The inclusion is injective, hence it is zero integrally. Classification of oriented plane bundles with boundary framing now gives a framing of the actual normal bundle agreeing with both preferred endpoint framings. This proves the required relative framing, rather than inferring it from absolute triviality.
Insert the product annulus into this framed neighborhood, as in step1.2. Its endpoint knots are the untwisted satellites because both endpoint framings are the preferred zero framings. In the TOP case the product model makes the new annulus locally flat; in the three smooth categories it is smooth. The ambient manifold is the original , so its homeomorphism or -homology conditions do not change. Thus the satellite assignment preserves concordance in all four categories and descends to the stated set maps.
Depends on
Used by
Dependency tree · two levels
6 results within two dependency steps of this one, each drawn at its shortest distance from it. An arrow runs from a result to what uses it, so the chart reads left to right and ends at this result, which carries a heavier outline. Every node is a link to that result. Click elsewhere on the chart to enlarge it.
Sources
- Asaf Karagila, Set Theory (2017 lecture notes) (standard reference, not scraped)
- Tim D. Cochran, Christopher W. Davis, and Arunima Ray, “Injectivity of satellite operators in knot concordance” (standard reference, not scraped)
- Michael H. Freedman and Frank Quinn, Topology of 4-Manifolds (standard reference, not scraped)