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2. N.A. Shanin, G.V. Davydov, S.Yu. Maslov, G.F. 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).