10 HGR:HCOLOR=3
20 XC=50:YC=50:R=30:GOSUB 30
25 END
30 X=R:Y=0:P=1-R:GOTO 100
40 Y=Y+1
50 IF P<=0 THEN P=P+2*Y+1:GOTO 70
60 X=X-1:P=P+2*Y-2*X+1
70 IF (X<Y) THEN RETURN
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 GOTO 40