MODE5:VDU5
FORU=0TO159
FORV=32TO223
x=U/64-1.25:y=V/128-1.1:z=1
x=x+y*.3:y=y-x*.3
X=0:Y=0.4:Z=-5
C=-1
REPEAT
D=SQR(X*X+Y*Y+Z*Z)
d=D-1
a=-d/(D*D*D)
x=x+X*a:y=y+Y*a:z=z+Z*a
n=1/(SQR(x*x+y*y+z*z))
x=x*n:y=y*n:z=z*n
B=Y+y*d
r=0
IFSGNY<>SGNB THENt=-Y/y:u=X+x*t:v=Z+z*t:r=u*u+v*v
X=X+x*d:Y=B:Z=Z+z*d
h=Z*1E4:h=h-INTh
IFr>2.25ANDr<14THENC=4-ABS(8-r)*.5-h
IFd<0.1THENC=0
IFD>6ORV<60ORV>200THENC=-3*(h>.98)
UNTILC>=0
GCOL0,C:PLOT69,U*8,V*4
NEXT,
REPEATUNTIL0
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