Undecidability of the exists*forall* Part of the Theory of Ground Term Algebra Modulo an AC Symbol.

Jerzy Marcinkowski Undecidability of the exists*forall* Part of the Theory of Ground Term Algebra Modulo an AC Symbol. 92-102 http://dx.doi.org/10.1007/3-540-48685-2_8 1999 conf/rta/1999 RTA db/conf/rta/rta99.html#Marcinkowski99