SubtractBlist( blist1, blist2 )
SubtractBlist subtracts the boolean list blist2 from the boolean list
blist1, which must have equal length. This is equivalent to assigning
blist1[i] := blist1[i] and not blist2[i] for all i.
SubtractBlist returns nothing, it is only called to change blist1.
gap> blist1 := [ true, true, false, false ];;
gap> blist2 := [ true, false, true, false ];;
gap> SubtractBlist( blist1, blist2 );
gap> blist1;
[ false, true, false, false ]
The function DifferenceBlist (see DifferenceBlist) is the
nondestructive counterpart to the procedure SubtractBlist.
GAP 3.4.4