A Change in Notation From now on, when we write Γ j= ', 22c:295 Seminar in AI — Decision Procedures we will assume that all the free variables of ' and of each formula in Γ are universally quantified. Rewriting This is done for convenience, but note that it does change the Cesare Tinelli meaning of j= for non-closed formulas.
[email protected] Example The University of Iowa Without implicit quantifiers: p(x) 6j= p(y). With the implicit quantifiers: p(x) j= p(y). Copyright 2004-05 — Cesare Tinelli and Clark Barrett. a a These notes were developed from a set of lecture notes originally written by Clark Barrett at New York University. These notes are copyrighted material and may not be used in other course settings outside of the University of Iowa in their current form or modified form without the express written permission of the copyright holders. Spring 04, 22c:295 Notes: Rewriting – p.1/25 Spring 04, 22c:295 Notes: Rewriting – p.3/25 Outline Rewriting • Rewriting Consider the general problem of establishing E j= s = t where E • Termination is a set of equations. • Completion Congruence closure handles the case when all equations are ground. (How?) Sources: There cannot be a simple procedure for the more general case Harrison, John. Introduction to Logic and Automated because first order logic with equality is, in general, undecidable. Theorem Proving. Unpublished manuscript. Used by permission. However, often the kind of equational reasoning needed is straightforward: equations are used in a predictable direction to simplify expressions. Using equations in a directional fashion is called rewriting, and there are indeed cases when this technique gives us a decision procedure.