The equation [X, U] + [y, V] = 0 in Free Lie Algebras. - Vladimir N. Remeslennikov; Ralph Stöhr (Int. J. Algebra Comput., 2007)

Products of Homogeneous Subspaces in Free Lie Algebras. - Ralph Stöhr; Michael R. Vaughan-Lee (Int. J. Algebra Comput., 2009)

On the Dimension of Products of Homogeneous Subspaces in Free Lie Algebras. - Nil Mansuroglu; Ralph Stöhr (Int. J. Algebra Comput., 2013)