Beitr\"age zur Algebra und Geometrie
Contributions to Algebra and Geometry
Volume 36 (1995), No. 1

Can You Recognize the Shape of a Figure from its Shadows?

J. Kincses and A. Kurusa

In connection with the Hammer's X-ray picture problem we discuss 
the following question: Given two convex compact sets
inside a circle such that the sets subtend equal angles at each point 
of the circle, is it then true that the
sets must coincide?