10 SCREEN 1
20 X = INT(RND(0) * 200)
30 Y = INT(RND(0) * 173)
40 FOR I=1 TO 20000
50 V = INT(RND(0) * 3) + 1
60 ON V GOTO 70,100,130
70 X = X/2
80 Y = Y/2
90 GOTO 150
100 X = 100 + (100-X)/2
110 Y = 173 - (173-Y)/2
120 GOTO 150
130 X = 200 - (200-X)/2
140 Y = Y/2
150 PSET X,Y,V
160 NEXT I