10 HGR:HCOLOR=3
20 XC=50:YC=50:R=30
30 X=0:Y=R:D=3-2*R:GOSUB 100
40 X=X+1
50 IF D>0 THEN Y=Y-1:D=D+4*(X-Y)+10:GOTO 70
60 D=D+4*X+6
70 GOSUB 100
80 IF Y>=X THEN 40
99 END
100 HPLOT XC+X,YC+Y
110 HPLOT XC-X,YC+Y
120 HPLOT XC+X,YC-Y
130 HPLOT XC-X,YC-Y
140 HPLOT XC+Y,YC+X
150 HPLOT XC-Y,YC+X
160 HPLOT XC+Y,YC-X
170 HPLOT XC-Y,YC-X
180 RETURN