gap>  V:=ContractibleGcomplex("PSL(4,Z)_d");
Non-free resolution in characteristic 0 for matrix group . 
No contracting homotopy available. 

gap> R:=FreeGResolution(V,5);
Resolution of length 5 in characteristic 0 for matrix group . 
No contracting homotopy available. 

gap> Size(R);
[ 18, 210, 1444, 26813 ]
