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The homotopy effect of a surgery killing a relative class below the middle
Statement
Assume . Let be a degree-one normal map with connected, let , and perform the -surgery on valid framed data representing , with result . For , for , and is the quotient of by the subgroup generated by the -translates of . When induces a fundamental-group isomorphism, in particular when is -connected, this subgroup is the -submodule generated by . For , the corresponding quotient uses the normal subgroup generated by those translates in the possibly nonabelian relative group ; when induces a fundamental-group isomorphism the relative group is abelian and has the usual -module formulation. For , the relative fundamental pointed set is the coset set for the source-image subgroup enlarged by the loop represented by the new core. No relative degree-zero group is asserted. The trace realizes these comparisons. In particular the usual -connected high-degree surgery step preserves lower relative groups and kills precisely the indicated generated class.
Facts & Assumptions
The represented sphere has an actual framing compatible with its prescribed stable normal data and gives a normal trace extension over the finite CW target. Stable normal data supplies framings of the surgery spheres below the middle dimension
A relative map cell gives the precise orbit-generated quotient, normal closure in degree two, and image-subgroup cosets in degree one. A relative map cell kills its class with the correct fundamental-group action
Lifting criterion for maps from path-connected locally path-connected spaces. Lifting criterion for maps from path-connected locally path-connected spaces
Long exact sequence of relative homotopy groups. Long exact sequence of relative homotopy groups
Proof
Given: Countable choice, valid normal-map surgery data, its trace , and .
Read the trace from : it is, relative to its incoming face, homotopy equivalent to with one -cell attached, and the map on its core is the specified nullhomotopy representing . This is the handle-core description in the normal-map surgery supplier. Apply the local relative-map-cell lemma. For it gives the orbit-generated quotient and the lower isomorphisms; for it gives the normal/action closure in the relative degree-two group, and for the enlarged-image coset description. The natural action is by unless the source and target fundamental groups have been identified.
Read the trace from : its single dual relative cell has dimension . Apply [F2] to this dual cell and the same trace extension, with source the connected smooth . It gives for , including every , with the degree-one comparison understood as a pointed-set comparison. The outgoing face is connected: its inclusion into the trace, whose incoming face is connected, has the homotopy type of an attachment of a cell of dimension , which cannot join distinct components. The dual-cell argument of [F2] smooths only inside that open cell and requires no supplied CW structure on . This compares relative map groups; the absolute inclusion need not be an isomorphism in degree , and no such stronger assertion is used.
Combine the two trace computations. If is an isomorphism, identify the orbit action with the target group-ring action. For in this case all relative degree-two boundaries lift to the universal covers; both covering spaces are simply connected, and the relative group is a quotient of the abelian absolute second homotopy group by the pair sequence, so it is abelian. Otherwise retain the normal-closure formulation. The -connected application for has the fundamental-group isomorphism automatically. These give every stated degree convention and the corrected quotient, with the exact borderline inequality .
Depends on
- The Axiom of Countable Choice ($\mathrm{AC}_\omega$)
- Degree-one normal map for the surgery program
- Stable normal data supplies framings of the surgery spheres below the middle dimension
- A relative map cell kills its class with the correct fundamental-group action
- Mapping cylinder and mapping cone
- Lifting criterion for maps from path-connected locally path-connected spaces
- Every nonempty path-connected locally path-connected semilocally simply connected space has a universal cover
- Long exact sequence of relative homotopy groups
Used by
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Sources
- Andrew Ranicki, Algebraic and Geometric Surgery (Oxford Mathematical Monographs, Oxford University Press 2002; complete electronic copy) (standard reference, not scraped)
- Wolfgang Lück, A Basic Introduction to Surgery Theory (complete lecture notes, ICTP/Münster) (standard reference, not scraped)