Description of Coordinate Groups of Irreducible Algebraic Sets over Free 2-Nilpotent Groups

Abstract: A convenient pure algebraic description of the coordinate groups of irreducible algebraic sets over a non-Abelian free 2-nilpotent group N of finite rank is given. Note that, in algebraic geometry over an arbitrary group N, it is natural to consider groups containing N as a subgroup (so-called N-groups) and homomorphisms of N-groups which are identical on N (N-homomorphisms). As a corollary, we describe all finitely generated groups H that are universally equivalent to N (with constants from N in the language). Additionally, we give a pure algebraic criterion determining when a finitely generated N-group H that is N-separated by N is, in fact, N-discriminated by N.