SET WINDOW -1,1,-1,1
INPUT PROMPT"何世代？":k
DRAW a(k) WITH SCALE(1/4^k)*SHIFT(-0.5,0.5)
DRAW a(k) WITH SCALE(1/4^k)*ROTATE(PI/2)*SHIFT(-0.5,-0.5)
DRAW a(k) WITH SCALE(1/4^k)*ROTATE(PI)*SHIFT(0.5,-0.5)
DRAW a(k) WITH SCALE(1/4^k)*ROTATE(3*PI/2)*SHIFT(0.5,0.5)
END
EXTERNAL PICTURE a(n)
IF n=0 THEN
   PLOT LINES:0,0;1,0
ELSE
   LET s=4^(n-1)
   DRAW a(n-1)
   DRAW a(n-1) WITH ROTATE(PI/2)*SHIFT(s,0)
   DRAW a(n-1) WITH SHIFT(s,s)
   DRAW a(n-1) WITH ROTATE(3*PI/2)*SHIFT(2*s,s)
   DRAW a(n-1) WITH ROTATE(PI/2)*SHIFT(2*s,-s)
   DRAW a(n-1) WITH ROTATE(PI)*SHIFT(3*s,-s)
   DRAW a(n-1) WITH ROTATE(3*PI/2)*SHIFT(3*s,0)
   DRAW a(n-1) WITH ROTATE(PI)*SHIFT(4*s,0)
END IF
END PICTURE