Timeline for Why is it true that if two 4-manifolds are homeomorphic then their squares are diffeomorphic?
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| Apr 13, 2016 at 15:48 | comment | added | Igor Belegradek | Speaking of an invariant: to get off the ground one has to find a $4$-manifold $X$ such that the map $d: X\to TOP/O$ is not null-homotopic. Then one could look at pairs of $4$-manifolds $X_1$, $X_2$ and see whether the associated map $d_1\times d_2$ stays homotopically non-trivial when projected to $TOP/O$ via the Whitney sum. | |
| Apr 13, 2016 at 15:01 | history | answered | Diarmuid Crowley | CC BY-SA 3.0 |