VRFA, chapter 8 (Routines), page 110

     Formal Argument rule

     Let `fa' be the Formal_arguments part  of  a  routine
     `r'   in   a   class   `C'.   Let  `formals'  be  the
     concatenation  of  every  Identifier_list  of   every
     Entity_declaration_group  in `fa'. Then `fa' is valid
     if  and  only  if  no  Identifier  `e'  appearing  in
     `formals' is the final name of a feature of `C'.