VMS Help FORTRAN, Statements, IMPLICIT_NONE  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  Inhibits the implicit declaration of data types in the program
  unit.  When it is used, you must declare the data types of all
  symbols explicitly.  You must not include any other IMPLICIT
  statements in the program unit.  containing an IMPLICIT NONE
  statement.  Statement format:

     IMPLICIT NONE

  NOTE:  To receive warnings when variables are used but not
  declared, you can specify the /WARNINGS=DECLARATIONS compiler
  option instead of IMPLICIT NONE.