VRRR, chapter 8 (Routines), page 113

     Routine rule

     A Routine part of a routine declaration is  valid  if
     and only if one of the following conditions holds:

        1 Its Routine_body is an Internal body  (beginning
          with do or once).

        2 In the other cases (where  the  Routine_body  is
          External   or  Deferred),  there  is  neither  a
          Local_declarations part nor a Rescue part.