PROC Trisect(b, a, c) IS 
  IF 
    VAR 
      d ~ (1, 0) REL (a, c), 
      e ~ (0.33, -0.2) REL (b, d), 
      f ~ (0.66, -0.2) REL (b, d) 
    IN 
      Geometry.Colinear(a, d, c) AND 
      (d, a) CONG (a, b) AND 
      (a, b) CONG (a, e) AND 
      (a, b) CONG (a, f) AND 
      (d, f) CONG (f, e) AND 
      (f, e) CONG (e, b) -> 
        PS.MoveTo(a); 
        PS.LineTo(b); 
        PS.MoveTo(a); 
        PS.LineTo(e); 
        PS.MoveTo(a); 
        PS.LineTo(f); 
        PS.MoveTo(a); 
        PS.LineTo(d) 
    END 
  FI 
END;