Author Archive: raphy

U. Haifa Topology & Geometry seminar: Wednesday, June 24, 2026, 13:00. Speaker: Emmanuel Farjoun (Hebrew University). Title: “Impossible functors, impossible natural transformations”.

Let us start with two very believable observations: 1. The only functors from the category of all sets to that of finite sets are the constant ones.2. Groups have no natural abelian subgroups.We raise questions about infinite categorical and space…
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Colloquium: June 23, 2026 (14:00, room 614). Speaker: Michael Brandenbursky (Ben Gurion). Title: “Lp-metrics on diffeomorphism groups: old and new results”.

Invariant metrics appear in most branches of mathematics. Examples include word metrics (entropy, fragmentation) and non-discrete metrics (Hofer norm and Lp) in symplectic, differential geometries and dynamics. In group theory examples include commutator length and primitive length. After providing some…
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U. Haifa Topology & Geometry seminar: Wednesday, May 6, 2026, 13:00. Speaker: Victor Turchin (Kansas State University). Title: “Graph-complexes and rational homotopy theory of embedding spaces”.

The homotopy groups of CW complexes and of the mapping spaces between them are notoriously difficult to compute. However, if one disregards torsion, rational homotopy theory is very effective and can easily solve such problems. Moreover, it produces efficient invariants…
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U. Haifa Topology & Geometry seminar: Wednesday, March 18, 2026, 13:00. Speaker: Vasily Dolgushev (Temple University). Title: “Grothendieck-Teichmuller shadows and their action on child’s drawings”.

In 1990, V. Drinfeld introduced the Grothendieck-Teichm¨uller group GT. This group receives the homomorphism from the absolute Galois group GQ of rational numbers and this homomorphism is injective due to Belyi’s theorem. Many challenging questions about GT are motivated by…
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U. Haifa Topology & Geometry seminar: Wednesday, March 11, 2026, 13:00. Speaker: William Balderrama (Bonn). Title: “Realization spaces and categorified square-zero deformation theory”.

A fundamental class of problems in algebraic topology are the realization problems: when is a given algebraic object realizable as an algebraic invariant of a space? For example, one might ask when a module over the Steenrod algebra arises as…
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