# Noon lecture

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On 5.4.2007 at 12:20 in S5, there is the following noon lecture:

# How many points can be reconstructed from k projections?

## Ales Privetivy

## KAM, MFF UK

## Abstract

How many points can be reconstructed from k projections? Ales Privetivy (joint work with Jiri Matousek and Petr Skovron)

Let A be an n-point set in the plane. A discrete X-ray of A in direction u gives the number of points of A on each line parallel to u. We define F(k) as the maximum number n such that there exist k directions u_1,...,u_k such that every set of at most n points in the plane can be uniquely reconstructed from its discrete X-rays in these directions. We establish a mildly exponential lower bound F(k)>2^((k/2)^(1/3)).

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