On the second cohomology group in semi-abelian categories (Q2463862)

Given a semi-abelian category the authors recall a definition of a homology of an object as it was given in a previous paper by the second author and T. Everaert. Using this definition the authors develop a five terms sequence generalising the five-term sequence of group cohomology to this general setting. An interpretation is given in terms of central extensions in this general context.