On the Closure Properties of the Class of Full G-models of a Deductive System

In this paper we consider the structure of the class FGMod S of full generalized models of a deductive system S from a universal-algebraic point of view, and the structure of the set of all the full generalized models of S on a fixed algebra A from the lattice-theoretical point of view; this set is represented by the lattice FACS s A of all algebraic closed-set systems C on A such that ( A , C ) ε FGMod S . We relate some properties of these structures with tipically logical properties of the sentential logic S . The main algebraic properties we consider are the closure of FGMod S under substructures and under reduced products, and the property that for any A the lattice FACS s A is a complete sublattice of the lattice of all algebraic closed-set systems over A. The logical properties are the existence of a fully adequate Gentzen system for S , the Local Deduction Theorem and the Deduction Theorem for S . Some of the results are established for arbitrary deductive systems, while some are found to hold only for deductive systems in more restricted classes like the protoalgebraic or the weakly algebraizable ones. The paper ends with a section on examples and counterexamples.