Superposition with Datatypes and Codatatypes

The absence of a finite axiomatization of the first-order theory of datatypes and codatatypes represents a challenge for automatic theorem provers. We propose two approaches to reason by saturation in this theory: one is a conservative theory extension with a finite number of axioms; the other is an extension of the superposition calculus, in conjunction with axioms. Both techniques are refutationally complete with respect to nonstandard models of datatypes and nonbranching codatatypes. They take into account the acyclicity of datatype values and the existence and uniqueness of cyclic codatatype values. We implemented them in the first-order prover Vampire and compare them experimentally.