Published online by Cambridge University Press: 20 November 2018
Let R be a commutative ring with unity and let M(R) be the multiplicative group of 4 x 4 triangular matrices (aij) over R, where a11 is a unit element of R and aii = 1 for i = 2, 3, 4. If V(=AN2 ∧ N2A) denotes the variety of groups which are both abelian-by-class-2 and class-2-by-abelian, then it is routine to verify that M(R) ∊ V. Here we prove the following,
Theorem. Let F(V) denote the free group of finite or countable infinite rank of the variety V. Then for a suitable choice of R, F(V) is embedded in M(R).