5 (null):X=-200:Y=0:Z=40:WI=10*(null)/180:F=10
10 A=7:MX=159:MY=99:DIM X(A),Y(A),Z(A)
15 GOSUB 1000
20 XX=0:XY=1:XZ=0
30 YX=0:YY=0:YZ=1
40 VX=10:VY=0:VZ=0:V=10:GOSUB 100
50 GET A$:IF A$="" THEN 50
52 IF A$="I" THEN X=X+20:GOTO 70
54 IF A$="," THEN X=X-20:GOTO 70
56 IF A$="J" THEN Y=Y-20:GOTO 70
58 IF A$="L" THEN Y=Y+20:GOTO 70
60 IF A$="+" THEN Z=Z+20:GOTO 70
62 IF A$="-" THEN Z=Z-20:GOTO 70
64 IF A$="O" THEN W=WI:GOSUB 600:GOTO70
66 IF A$="U" THEN W=-WI:GOSUB 600
70 GOSUB 100
80 GOTO 50
100 (null):T=1
110 GOSUB 300:EX=KX:EY=KY
120 FOR T=2 TO A
130 AX=KX:AY=KY
140 GOSUB 300
150 (null) KX,KY,AX,AY
160 NEXTT
170 (null) KX,KY,EX,EY
180 RETURN
300 BX=X(T)-X:BY=Y(T)-Y:BZ=Z(T)-Z
310 L=SQR(BX*BX+BY*BY+BZ*BZ)
320 IF L<=V THEN RETURN
330 DX=BX-VX:DY=BY-VY:DZ=BZ-VZ
340 IF SQR(DX*DX+DY*DY+DZ*DZ)>=L THEN RETURN
350 D=BX*XY*YZ+XX*YY*BZ+YX*BY*XZ-BZ*XY*YX-XZ*YY*BX-YZ*BY*XX
360 D2=-BX*VY*YZ-VX*YY*BZ-YX*BY*VZ+BZ*VY*YX+VZ*YY*BX+YZ*BY*VX
370 D3=-BX*XY*VZ-XX*VY*BZ-VX*BY*XZ+BZ*XY*VX+XZ*VY*BX+VZ*BY*XX
380 KY=MY-D3/D*F
390 KX=MX+D2/D*F
400 RETURN
600 OX=VX:OY=VY:GOSUB 650
610 VX=NX:VY=NY
620 OX=XX:OY=XY:GOSUB 650
630 XX=NX:XY=NY:RETURN
650 NX=OX*COS(W)-OY*SIN(W)
660 NY=OY*COS(W)+OX*SIN(W)
670 RETURN
1000 FOR T=1 TO A
1010 READ X(T),Y(T),Z(T)
1020 NEXTT
1030 RETURN
2000 DATA -50,-50,0
2010 DATA 50,-50,0
2020 DATA 50,50,0
2030 DATA -50,50,0
2040 DATA -50,-50,0
2050 DATA 0,0,0
2060 DATA 0,0,70