_X:=ContractibleGcomplex("SL(2,O-2)");;
Z2:=Group( -Identity(_X!.group) );;
Y:=QuotientOfContractibleGcomplex(_X,Z2);;
R:=FreeGResolution(Y,21);;
K:=TensorWithIntegersModP(R,2);;
L:=List([0..20],n->Homology(K,n));;
p:=PoincareSeries(L,20);
Print(p,"\n");
