1. Semantics and termination of non-deterministic recursive programs;De Bakker,1976
2. Recursive definitions of partial functions and their computations;Cadiou,1972
3. A Mathematical Model for Nondeterministic Computations;Egli,1975
4. Backtracking in recursive computations;Francez;Acta Inform.,1977
5. Mathematical Theory of Computation;Manna,1974