
  We wrote : “ If  is an unknown type , then the no - occurrence invariant tells us
;; that it is not bound in the substitution.” Explain in detail why this is so.

  if  is an unknown type and it is bound in the substitution . the substitution left side will also
;; be an unknown type.

 that it is not bound in the substitution.” Explain in detail why this is so.
 be an unknown type.

  We wrote : “ If  is an unknown type , then the no - occurrence invariant tells us

  if  is an unknown type and it is bound in the substitution . the substitution left side will also
