Decidability of behavioural equivalence in unary PCF

Unary PCF is Decidable

We show that unary PCF, a very small fragment of Plotkin’s PCF [?], has a decidable observational pre-order, and that its fully abstract model is effectively presentable. This is in marked contrast to larger fragments, where corresponding results fail [?]. The techniques used are adaptions of those of Padovani [?], who applied them to the minimal model of the simply typed lambda calculus.

Relative Definability and Models of Unary PCF

Decidability of Split Equivalence

We show that the following problem is decidable: given expressions E1 and E2 constructed from variables by the regular operations and shuffle, is the identity E1 = E2 true for all instantiations of its variables by strings? Our proof uses the notations developed in the causal approach to concurrency. As a byproduct we obtain decidability of similar equivalence for other formalisms. In particula...

Decidability of DPDA equivalence

A proof of decidability of equivalence between deterministic pushdown automata is presented using a mixture of methods developed in concurrency and language theory. The technique appeals to a tableau proof system for equivalence of configurations of strict deterministic grammars.

An Introduction to Decidability of DPDA Equivalence