Conditionally transfers control to one of three statements, based
  on the current value of an arithmetic expression.  Statement
  format:

     IF (e) s1,s2,s3

     e         Is an arithmetic expression.

     s1,s2,s3  Are labels of executable statements in the same
               program unit.  All three labels are required,
               but they need not refer to different statements.

  Executes the statement at the first label ("s1") if the arithmetic
  expression evaluates to a value less than 0; the statement at the
  second label ("s2") if the arithmetic expression evaluates to 0; or
  the statement at the third label ("s3") if the arithmetic
  expression evaluates to a value greater than 0.

                                 NOTE

          The  arithmetic  IF  statement  is  an  obsolescent
          feature  in  Fortran  95  and  Fortran  90.  HP
          Fortran fully supports this feature.