Well-Nested Context Unification. Proc. of the 20th Int. Conf. on Automated Deduction (CADE-20). Well-Nested Context Unification ⋆

Abstract. Context unification (CU) is the open problem of solving context equations for trees. We distinguish a new decidable variant of CU – well-nested CU – and present a new unification algorithm that solves well-nested context equations in non-deterministic polynomial time. We show that minimal well-nested solutions of context equations can be composed from the material present in the equation (see Theorem 1). This property is wishful when modeling natural language ellipsis in CU.