ELEMENTARY FORMAL SYSTEM AS A LOGIC PROGRAMMING LANGUAGE

In this paper, we give a theoretical foundation of EFS (elementary formal system) as a logic programming language. We show that the set of all the unifiers of two atoms is finite and computable by restricting the form of axioms and goals without losing generality. The restriction makes the negation as failure rule complete. We give two conditions of EFS's such that the negation as failure rule is identical to the closed world assumption. We also give a subclass of EFS's where a procedure of CWA is given as bounding the length of derivations We compare these classes with the Chomsky hierarchy.