10 CLS 
15 CROFF 
20 x=2:y=2:a=0:b=0
30 POS x,y:PRINT " ";
40 IF a=0 THEN x=x+2
50 IF a=1 THEN x=x-2
60 IF b=0 THEN y=y+2
70 IF b=1 THEN y=y-2
75 POS x,y:PRINT CHR$ (15);
80 IF x>37 THEN a=1:BEEP 77
90 IF x<1 THEN a=0:BEEP 99
100 IF y>27 THEN b=1:BEEP 88
110 IF y<1 THEN b=0:BEEP 66
170 GOTO 30