Groups whose word problems are not semilinear

Suppose that G is a finitely generated group andWP(G) is the formal language ofwords defining the identity in G. We prove that if G is a virtually nilpotent group that is not virtually abelian, the fundamental group of a finite volume hyperbolic three-manifold, or a right-angled Artin groupwhose graph lies in a certain infinite class, then WP(G) is not a multiple context-free language.