In this paper, we will be
concerned with topological group extensions of a polonais group A by a polonais
group G. When A is abelian, we will consider two cohomology groups: H2(G,A) and
HV2(G,A).H2(G,A) is based on Borel cochains and was studied by Moore.
HV2(G,A) is obtained by identifying cochains which differ only on a first category
set, an idea suggested to us by D. Wigner. We will show that each of the groups
classifies the extensions and that the hypothesis that A be abelian can be
eliminated.