gap> K:=BianchiGcomplex(-23);;

gap> chi:=0;;
gap> for n in [0..2] do
> for k in [1..K!.dimension(n)] do
> g:=Order(K!.stabilizer(n,k));
> if g &lt; infinity then chi:=chi + (-1)^n/g; fi;
> od;od;
gap> chi;
0
