Orateur
Mariam Pirashvili
Description
Crossed modules are algebraic models of homotopy 2-types and hence have \pi_1 and \pi_2 . We propose a definition of the centre of a crossed module whose essential invariants can be computed via the group cohomology H^i (\pi_1, \pi_2). This definition therefore has much nicer properties than one proposed by Norrie in the 80’s.
