anchor.diff:      interface
           subroutine plgvpd( xmin, xmax, ymin, ymax )
               use plplot_types
  +            implicit none
               real(kind=plflt) :: xmin, xmax, ymin, ymax
           end subroutine plgvpd
       end interface
  
positive.code:     interface
          subroutine plszax( digmax, digits )
              use plplot_types
              integer(kind=plint) :: digmax, digits
          end subroutine plszax
      end interface
  
negative.code:     interface
          subroutine plpath( n, x1, y1, x2, y2 )
              use plplot_types
              implicit none
              integer(kind=plint) :: n
              real(kind=plflt) :: x1, y1, x2, y2
          end subroutine plpath
  