10 GRAPHICS 8:COLOR 1
20 R=40:CX=150:CY=100
30 X=0:Y=R:D=5-(4*R):DA=12:DB=20-(8*R)
40 PLOT CX+X,CY+Y:PLOT CX+X,CY-Y:PLOT CX-X,CY+Y:PLOT CX-X,CY-Y
45 PLOT CX+Y,CY+X:PLOT CX+Y,CY-X:PLOT CX-Y,CY+X:PLOT CX-Y,CY-X
50 IF D<0 THEN D=D+DA:DB=DB+8:GOTO 70
60 IF D>0 OR D=0 THEN Y=Y-1:D=D+DB:DB=DB+16
70 X=X+1:DA=DA+8
80 IF X<Y THEN GOTO 40