Let H be a group, let {G1: i ∈ I} be a set of groups and, for each i, let θi be a a monomorphism: H → G1, with Hθ1 = H1. We call such a system of groups and monomorphisms an amalgam and denote it by [G1; H; θi; Hi]. By an embedding of the amalgam into a group G is meant a set of monomorphisms ϕi: G1 → G such that θiϕi= θjϕjfor all i, j and G1ϕi = Hθϕk, for all i, j, k.