TO PDP4 :S
   PD
   SETPC 7
   SETPENSIZE 3
   FD :S * 3.5 
   WAIT 60 RT 135
   FD :S * 3.5 * SQRT 2
   WAIT 60 LT 45
   FD :S * 4.0
   WAIT 60 RT 45
   FD :S * 8.0 * SQRT 2
   WAIT 60 RT 135
   FD :S * 4.0
   WAIT 60   RT 45
   FD :S * 3.5 * SQRT 2
   WAIT 60   LT 135
   FD :S * 3.5
   WAIT 60   RT 90
   FD :S * 4.5 
   WAIT 60   LT 135
   FD :S * 4.5 * SQRT 2
   WAIT 60   RT 45
   FD :S * 4.0
   WAIT 60   RT 135
   FD :S * 8.0 * SQRT 2
   WAIT 60   RT 45
   FD :S * 4.0
   WAIT 60   LT 45
   FD :S * 4.5 * SQRT 2
   WAIT 60   RT 135
   FD :S * 4.5
END

TO HGRID :S
   FD 100 * :S BK 100 * :S
   PU RT 90 FD :S LT 90 PD
END
TO VGRID :S
   FD 100 * :S BK 100 * :S
   PU LT 90 FD :S RT 90 PD
END

TO GRID :S
   WINDOW CS
   SETPC 2
   SETPENSIZE 1
   PU HOME  LT 90 FD 500 RT 90 FD 500 PD
   RT 90 REPEAT 100 [ HGRID :S ]
   PU HOME LT 90 FD 500 RT 90 FD 500 PD
   RT 180 REPEAT 100 [ VGRID :S ]
END

GRID 20
PU HOME FD 160
PDP4 20
HIDETURTLE