Wednesday, October 28 |
Geometry and Topology
Time: 15:30
Speaker: Bob Lutz (MSRI Berkeley) Title: "Teaching a new dog old tricks: Classical topology theorems in the discrete setting" Room: Zoom Meeting ID: 958 6908 4555 Abstract: An exciting theme in combinatorics is degenerating a continuous theory into a discrete one and asking which features of the original are preserved. This talk will focus on our effort to replicate classical theorems of topology in the setting of discrete homotopy and singular homology theories for graphs. These combinatorial theories have a distinct cubical flavor, with the roles of spheres and simplices played by grids and hypercube graphs. A major goal has been to connect the two by way of a discrete Hurewicz theorem. Our first result marks progress toward this goal: We will describe a natural map from discrete homotopy to discrete homology, and show that it is surjective in a large number of cases. As a corollary, we prove the existence of nontrivial higher discrete homotopy groups. Our second result is a discrete version of a theorem of P. A. Smith, which says that the fundamental group of a nontrivial symmetric product of $X$ is isomorphic to the first homology group of $X$. |
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