Ck. Gupta et Uu. Umirbaev, Systems of linear equations equations over associative algebras and the occurrence problem for Lie algebras, COMM ALGEB, 27(1), 1999, pp. 411-427
In this paper we solve the algorithmic problem of recognizing the compatibi
lity of a system of linear equations over a free associative algebra of the
variety M-k defined by the identity [x(1), y(1)][x(2), y(x)] ... [x(k), y(
k)] = 0, which is then used to prove that the free NcU-Lie algebras have th
e solvable occurrence problem.