  We consider the problem of minimizing the size of a family of sets G such
that every subset of 1,...,n can be written as a disjoint union of at most k
members of G, where k and n are given numbers. This problem originates in a
real-world application aiming at the diversity of industrial production. At the
same time, the minimum of G so that every subset of 1,...,n is the union of two
sets in G has been asked by Erdos and studied recently by Furedi and Katona
without requiring the disjointness of the sets. A simple construction providing
a feasible solution is conjectured to be optimal for this problem for all
values of n and k and regardless of the disjointness requirement; we prove this
conjecture in special cases including all (n,k) for which n <= 3k holds, and
some individual values of n and k.
