Idealized Algol with ground recursion, and DPDA Equivalence

Abstract

We prove that observational equivalence of IA3 + Y0 (3rd-order Idealized Algol with 0th-order recursion) is equivalent to the DPDA Equivalence Problem, and hence decidable. This completes the classification of decidable fragments of Idealized Algol. We also prove that observational approximation of IA1 + Y0 is undecidable by reducing the DPDA Containment Problem to it. © Springer-Verlag Berlin Heidelberg 2005.