How can I define cas function of an operator(mathematical term)?

[Albert Chan]

HP Prime cannot generate unique symbol, like lisp gensym. (correct this if I was wrong ...)
Here, we use a fixed-name global symbol as a bridge.

If symbol is then used for other purpose, we may get into trouble.
See thread, HP Prime undef for Limes. Maybe a Bug?

Code:

#CAS
MYINT(f,x) :=
BEGIN
subst(int(f(x=x_), x_), x_=x);
END;
#END

CAS> MYINT(x*sin(y), x)      → 1/2*x^2*sin(y)
CAS> MYINT(x*sin(y), y)      → -x*cos(y)
CAS> MYINT(x*sin(y), z)      → x*z*sin(y)

Update: removed ASSUME(x_, symbol).