1. Galyna Dobrovolska, John Kim, and Xiaoguang Ma, On the lower central series of an associative algebra (with an appendix by Pavel Etingof), J. Algebra 320 (2008), no. 1, 213–237.[MR]
  2. Pavel Etingof, John Kim, and Xiaoguang Ma, On universal Lie nilpotent associative algebras, J. Algebra 321 (2009), no. 2, 697–703.[MR/doi]