PROC FillRed() IS 
  PS.SetRGB(1, 0, 0); PS.Fill() 
END;

PROC EqTr(a, b) IS 
  IF 
    VAR 
      c ~ (0.5, 0.866) REL (a, b) 
    IN 
      (a, b) CONG (b, c) AND 
      (b, c) CONG (c, a) -> 
        PS.MoveTo(a); 
        PS.LineTo(b); 
        PS.LineTo(c); 
        PS.Close() 
    END 
  FI 
END;

PRED HorSym(a, b, c) IS 
  c HOR b AND (c, a) CONG (a, b) 
END;