100 SCREEN 1:RANDOMIZE 0:DIM X(3),Y(3)
  110 FOR I=0 TO 3:READ X(I),Y(I):NEXT :DATA 1,0, 0,1, -1,0, 0,-1
  120 A=160:B=100:V=0:LINE (0,0)-(351,223),0,BF
  130 A=A+X(V):B=B+Y(V)
  140 IF POINT(A,B)>0 THEN PSET (A,B),0:V=(V+1) AND 3 ELSE PSET (A,B),32767:V=(V-1) AND 3
  150 GOTO 130