We consider the problem of combining procedures that decide solvability of (dis)uniication problems over disjoint equational theories. Partial answers to the following questions are given: Which properties of the component theories imply intractability in the sense that there cannot be a polynomial combination algorithm, assuming P 6 = NP? Which general properties of the component theories guar...

The Haskell Equational Reasoning Assistant (HERA) is an application written in Haskell that helps users construct and present equational reasoning style proofs[1]. In this paper we discuss the technology behind the user interface.

Freyd and Scedrov showed that the equational theory of representable allegories (essentially those allegories which have a settheoretic representation as relations) is decidable. This paper proves that the pure equational theory of allegories is decidable.