> A:=Matrix([[a,b],[c,d]]);

> B:=Matrix([[p,q],[r,s]]);

> B := _rtable[16238716];

> A.B-B.A;

AB=BA <=> AB-BA=0 <=> b=0 ¥B c=0 <=> A ¬O¹ï¨¤¤Æ¯x°}