DO
   LET k=k+1
   SET WINDOW 0,2^(k-1),0,2^(k-1)
   DRAW gas(k)
   WAIT DELAY 1
LOOP
END
EXTERNAL PICTURE gas(n)
IF n=1 THEN
   PLOT LINES:0,0;1,0;0.5,SQR(3)/2;0,0
ELSE
   LET s=2^(n-2)
   DRAW gas(n-1)
   DRAW gas(n-1) WITH SHIFT(s,0)
   DRAW gas(n-1) WITH SHIFT(s/2,SQR(3)*s/2)
END IF
END PICTURE