Sergei G. Vorobyov. forall exists*-Equational Theory of Context Unification is Pi::1:::::0:::-Hard. In Lubos Brim, Jozef Gruska, Jirí Zlatuska, editors, Mathematical Foundations of Computer Science 1998, 23rd International Symposium, MFCS 98, Brno, Czech Republic, August 24-28, 1998, Proceedings. Volume 1450 of Lecture Notes in Computer Science, pages 597-606, Springer, 1998. [doi]
Abstract is missing.