Matchings in arbitrary groups

Abstract

A matching in a group G is a bijection φ from a subset A to a subset B in G such that a φ ( a ) ∉ A for all a ∈ A . The group G is said to have the matching property if, for any finite subsets A , B in G of same cardinality with 1 ∉ B , there is a matching from A to B. Using tools from additive number theory, Losonczy proved a few years ago that the only abelian groups satisfying the matching property are the torsion-free ones and those of prime order. He also proved that, in an abelian group, any finite subset A avoiding 1 admits a matching from A to A. In this paper, we show that both Losonczy's results hold verbatim for all groups, not only abelian ones. Our main tools are classical theorems of Kemperman and Olson, also pertaining to additive number theory, but specifically developed for possibly nonabelian groups.