Tatyana A. Novikova, Vladimir A. Zakharov. Two-sided unification is NP-complete. In Temur Kutsia, Christophe Ringeissen, editors, Proceedings of the 28th International Workshop on Unification, UNIF 2014, Vienna, Austria, July 13, 2014. pages 55-61, 2014. [doi]
Abstract is missing.