10 DEF FNz=-LOG(SQR(x*x+y*y))
20 ed=10:sf=500:st=0.1:ax=60:az=70
30 e$=CHR$(27):cl$=e$+"E"+e$+"H":PRINT eS"f
40 PRINT cl$:DEFINT h-k:DIM h(720)
50 xc=360:yc=124:pi=3.14159:ax=ax*pi/180:az=az*pi/180
60 v1=-SIN(az)*2:v2=-COS(az)*COS(ax):v3=-C0S(az)*SIN(ax)
70 v4=COS(az):v5=-SIN(az)*COS(ax):v6=-SIN(az)*SIN(ax)
80 v7=SIN(ax):v8=-C0S(ax):POKE 441,0:GOSUB 270
90 FOR y=2 TO -2 STEP -st:flag=0
100 FOR x=2 TO -2 STEP -st:z=FNz
110 IF flag=0 THEN flag=1:GOSUB 250:GOTO 190
120 GOSUB 250
130 dy=sy-ty:dx=sx-tx:n=dy/dx:nx=SGN(dx):ny=SGN(dy)
140 IF ABS(n)>1 THEN n=1/n:GOTO 170
150 FOR tx=tx TO sx STEP nx:ty=ty+n*nx
160 GOSUB 200:NEXT:GOTO 190
170 FOR ty=ty TO sy STEP ny:tx=tx+n*ny
180 GOSUB 200:NEXT
190 tx=sx:ty=sy:NEXT x,y:PRINT e$"e":END
200 a%=INT(tx):b%=INT(ty)
210 IF a%<0 OR a%>719 OR b%<0 OR b%>247 THEN 240
220 IF b%<h(a%) THEN 240
230 CALL plot(a%,b%):h(a%)=b%
240 RETURN
250 ex=x*v1+y*v4:ey=x*v2+y*v5+z*v7:ez=x*v3+y*v6+z*v8+ed
260 sx=ex*sf/ez+xc:sy=ey*sf/ez+yc:RETURN
270 MEMORY &HBFFF:plot=&HC000:a=plot:e=0
280 RESTORE 400
290 FOR f=0 TO 14
300 s=0
310 FOR g=0 TO 7
320 READ x$:x=VAL("&H"+x$)
330 s=s+x:POKE a,x:a=a+1:NEXT
340 READ x$
350 IF s<>VAL("&H"+x$) THEN e=e+1:PRINT "Error in Line";10*(f+40)
360 NEXT
370 IF e=0 THEN RETURN
380 PRINT e; "ERROR";:IF e=1 THEN PRINT ELSE PRINT "s"
390 STOP
400 DATA 0A,32,7C,C0,4E,23,46,21,250
410 DATA CF,02,A7,ED,42,D8,ED,43,4AF
420 DATA 78,C0,EB,5E,23,56,7A,A7,41B
430 DATA C0,93,3D,5F,ED,53,7A,C0,469
440 DATA F3,ED,73,7D,C0,31,9D,C0,51E
450 DATA 01,36,C0,CD,5A,FC,E9,00,403
460 DATA ED,7B,7D,C0,FB,C9,2A,7A,50D
470 DATA C0,29,11,00,B6,19,5E,23,24A
480 DATA 56,7B,E6,F8,CB,27,CB,12,47E
490 DATA 47,7B,E6,07,B0,5F,2A,78,360
500 DATA C0,45,7D,E6,F8,6F,EB,19,4D3
510 DATA 78,E6,07,3C,47,AF,37,1F,2ED
520 DATA 10,FD,47,3A,7C,C0,A7,20,391
530 DATA 05,78,2F,A6,77,C9,3D,78,347
540 DATA 20,03,B6,77,C9,AE,77,C9,407