Topological structure group and cell-like maps
The structure set SCAT(X) of the Poincare complex X measures the number of distinct CAT-manifolds in the simple homotopy class of X where CAT is the category.
Contrary to the DIFF, in the case of topological manifolds STOP(M) is a group.
We define a subset SCE(M)⊂STOP(M) generated by homotopy equivalences h:N→M that come as homotopy lifts of g in the diagram Ng→Xf←M
where f and g are cell-like maps.
We give a complete description of SCE(M). In particular we prove the following
THEOREM. For any manifold M the set SCE(M) is a group.
For a simply connected manifold M with finite π2(M) the group SCE(M) equals the odd torsion subgroup of STOP(M).
As a corollary we construct two smooth nonhomeomorphic manifolds that admit cell-like maps with the same image.
We use this result to construct exotic convergence of Reimannian manifolds in the Gromov-Hausdorff moduli space of manifolds with fixed contractibility function.
This is a joint work with Steve Ferry and Shmuel Weinberger.