Colloquium: Monday, October 30, 4 pm. Speaker: Yuval Ginosar (Haifa). Title: “Extensions and Obstructions”.

Let N be a normal subgroup of a group G. When does a homomorphism from N to an abelian group A extend to a homomorphism from G to A?  When does an irreducible (projective) representation f of N extend to G and what are the irreducible projective representations of G that lie above f?  It turns out that obstructions to the existence of such extensions lie in an abelian group determined by the quotient G/N.
In this talk we present a generalization of this obstruction theory to a broad family of group graded algebras and show its applications to structure theorems about simply-graded algebras.