vars oplan_terminal_type; undef -> oplan_terminal_type;

define clearscreen;
  comment can be done with
          vedscreenclear() vedscreenflush() if VED present;
  comment can be done in a terminal independent way on UNIX with
          sysobey('clear');
  comment can be done in a Windows Command Window with sysobey('cls');
  comment can be done slowly on any system by scrolling the screen up n lines
          nl(n);
  comment can be done with rawcharout of appropriate characters for the
          particular VDU in use followed by a flush and delay if needed
          rawcharout(<code>) ...  sysflush(popdevraw) syssleep(<ms delay>);
  comment particular form that follows may be altered before NONLIN creation;

  if oplan_terminal_type == undef then
    systranslate('$TERM') -> oplan_terminal_type;
  endif;

  switchon oplan_terminal_type
    case = 'xterm' or 'vt100' then
      rawcharout(27);      rawcharout(`[`);      rawcharout(`;`);
      rawcharout(`H`);     rawcharout(27);       rawcharout(`[`);
      rawcharout(`2`);     rawcharout(`J`);
    else
      rawcharout(12);  ;;; simple Form Feed.
  endswitchon;

  sysflush(popdevraw);
  syssleep(1);
enddefine;