2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/31826A simple mathematical definition of the 4-port model for pure Prolog is given. The model combines the intuition of ports with a compact representation of execution state. Forward and backward derivation steps are possible. The model satisfies a modularity claim, making it suitable for formal reasoning.15 pages. Appeared in Proc. of the 5th Workshop on Rule-Based Constraint Reasoning and Programming (RCoRP'03), within CP'03, Kinsale, September 2003Programming LanguagesLogic in Computer ScienceF.3.2; F.3.1; D.2.5; I.2.3text