gap> K:=ContractibleGcomplex("SL(3,Z)s");;
gap> G:=HAPCongruenceSubgroupGamma0(3,101);;
gap> Y:=GComplexToRegularCWComplex(K,G);;

gap> C:=ChainComplexOfRegularCWComplex(Y);
Chain complex of length 3 in characteristic 0 . 

gap> List([0..3],C!.dimension);
[ 3679, 37565, 75083, 41212 ]

gap> D:=ContractedComplex(C);time;
Chain complex of length 3 in characteristic 0 . 

170547

gap> List([0..3],D!.dimension);
[ 1, 27, 78, 67 ]

gap> List([0..3],n->Homology(D,n));time;
[ [ 0 ], [ 25 ], [ 2, 2, 2, 2, 2 ], 
  [ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 ] ]
26
