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Tuesday, 30.11.2021 | 14.15 Uhr - 15.45 Uhr

Oberseminar Geometrische Analysis und Zahlentheorie


Damian Osajda (University of Wroclaw)


Helly graphs and their automorphism groups


A graph is Helly if each family of pairwise intersecting (combinatorial) balls has non-empty intersection. Groups acting geometrically on such graphs are themselves called Helly. The family of such groups is vast, it contains: Gromov hyperbolic groups, CAT(0) cubical groups, Garside groups, FC type Artin groups, and others. On the other hand, being Helly implies many important algorithmic and geometric features of the group. In particular, such groups act geometrically on spaces with convex geodesic bicombing, equipping them with a kind of CAT(0)-like structure. I will present basic properties and examples of Helly groups. The talk is based on joint works with Jeremie Chalopin, Victor Chepoi, Anthony Genevois, Hiroshi Hirai, Jingyin Huang, Motiejus Valiunas, Thomas Haettel.



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