10 CLS0
20 X=RND(32)-1
30 Y=RND(16)-1
40 Z=RND(9)-1
50 GOSUB90
60 GOTO 20
90 IFZ=0 OR RND(7)=3THEN150
100 SET(31-X,16+Y,Z)
110 SET(31-X,15-Y,Z)
120 SET(32+X,16+Y,Z)
130 SET(32+X,15-Y,Z)
140 RETURN
150 RESET(31-X,16+Y)
160 RESET(31-X,15-Y)
170 RESET(32+X,16+Y)
180 RESET(32+X,15-Y)
190 RETURN