## Abstract

Gelfond and Lifschitz introduce a declarative language $\cal A$ for describing effects of actions and describe translations of theories in this language into extended logic programs. In this paper we extend the language $\cal A$ and its translation to allow reasoning about the effects of concurrent actions. The logic programming formalization of situation calculus with concurrent actions presented in the paper is of independent interest and may serve as a test bed for the investigation of various transformations and logic programming inference mechanisms.