Let a homogeneous solid contain a convex hole and take x-rays so that the "darkness" at each point
on a photographic plate determines the length of the chord of along the line of propagation of an x-ray. Then how many x-ray
pictures must be taken to exactly reconstruct if
1. The x-rays originate from a point source,
2. The x-rays originate from a source at infinity and so are parallel?
Croft, H. T.; Falconer, K. J.; and Guy, R. K. "Hammer's X-Ray Problems." §A2 in Unsolved
Problems in Geometry. New York: Springer-Verlag, pp. 11-14, 1991.
and take x-rays so that the "darkness" at each point
on a photographic plate determines the length of the chord of 
along the line of propagation of an x-ray. Then how many x-ray
pictures must be taken to exactly reconstruct 
if
