M. Coppo and F. Cardone

Decidability properties of recursive types

In ICTCS'03, volume 2841 of LNCS, pages 242-255 Springer-Verlag, 2003


In this paper we study decision problems and invertibility for two notions of equivalence of recursive types. In particular, for recursive types presented by means of a recursion operator mu, we describe an algorithm showing that the natural equivalence generated by finitely many steps of folding and unfolding of mu-types is decidable. For recursive types presented by finite systems of recursive equations, we give a thoroughly coinductive characterization of the equivalence induced by their interpretation as infinite (regular) trees, from which the decidability of this equivalence follows. A formal proof of the former result, to our knowledge, has never appeared in the literature. The latter result, on the contrary, is well known but we present here a new proof obtained as an application of general coalgebraic facts to the theory of recursive types. From these results invertibility is easily proved for both equivalences.


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