modules.lib
LIB "modules.lib"; ring r; matrix ma[2][2]=x,y,x,y; Matrix M=ma; matrix na[2][1]=-y,x; Matrix N=na; M; ==> {1} {1} ==> {0} x y ==> {0} x y ==> N; ==> {1} ==> {0} -y ==> {0} x ==> N==M; ==> 0 M==M; ==> 1