Comparing Matrices (in CAS Mode?)

[Eddie W. Shore]

I am trying create a matrix program in CAS mode, isorthogonal, to test whether a matrix is orthogonal:

#cas
isorthogonal(m):=
BEGIN
LOCAL s,n,p;
s:=SIZE(m);
s:=s(1);
n:=IDENMAT(s);
p:=simplify(TRN(m)*m));
IF n==p THEN
RETURN 1;
ELSE
RETURN 0;
END;
END;
#end

Testing [[2,0][0,2]] and [[2*x,0][0,2*x]] I get the error

"For: Unable to check test Error: Bad Argument Value"

Are we not able to compare matrices in CAS mode? Thanks,

Eddie