1. C. Berge, Theory of Graphs and Its Applications [Russian translation], IL, Moscow (1962).
2. N. A. Shanin, G. V. Davydov, S. Yu. Maslov, G. E. Mints, V. P. Orevkov, and A. O. Slisenko, An Algorithm for a Computer-Aided Search for Natural Logical Proofs in the Predicate Calculus [in Russian], “Nauka,” Moscow (1965).
3. J. A. Robinson, “A machine-oriented logic based on the resolution principle,” J. Assoc. Computing Mach., 12(1):23–41 (1965).