VNCH, chapter 13 (Conformance), page 226

     An  expression  `v'  of  type  `VT'  conforms  to  an
     expression  `t'  of  type  `TT'  if  and only if they
     satisfy any one of the following four conditions.

        1 `VT' conforms to `TT'.

        2 `TT' is `like v' (`v' in this case  must  be  an
          entity).

        3 `VT' and `TT' are both of the form  like  x  for
          the same `x'.

        4 `TT' is like x where `x' is a formal argument to
          a  routine  `r',  `v' is an actual argument in a
          call to `r', and `VT' conforms to  the  type  of
          the  actual argument corresponding to `x' in the
          call.