gap> gamma:=HAP_PrincipalCongruenceSubgroup(5);;
gap> K:=ContractibleGcomplex("SL(2,Z)");;
gap> K:=BarycentricSubdivision(K);;K:=BarycentricSubdivision(K);;
gap> Y:=GComplexToRegularCWComplex(K,gamma);;
gap> Homology(Y,1);
[ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 ]
gap> Display( GraphOfRegularCWComplex( Y ));
