gap> B:=ContractedComplex(D);
Chain complex of length 2 in characteristic 0 . 

gap> Size(B);
20
gap> Homology(B,1);
[ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 ]
