Yates, R. A., Hart, T. P., & Raphael, B. (1970). Resolution graphs. SRI INTERNATIONAL MENLO PARK CA.
This paper introduces a new notation, called “resolution graphs,” for deduction by resolution in first-order predicate calculus. A resolution graph consists of groups of nodes that represent initial clauses of a deduction and links that represent unifying substitutions. Each such graph uniquely represents a resultant clause that can be deduced by certain alternative but equivalent sequences of resolution and factoring operations.