The beginning of logic programming can be attributed to Kowalski and Colmerauer. Kowalski formulated the procedural interpretation of Horn clause logic and showed that the axiom A if B can be read as a procedure of a recursive programming language, where A is the procedure head and B is its body. At the same time, early 1970's, Colmerauer and his group at the University of Marseille-Aix developed a specialized theorem prover, which they used to implement natural processing systems. The theorem prover, they called it PROLOG (for Programation et Logique or Programming in Logic), embodied Kowalski's procedural interpretation.