William McCune

OTTER 3.0 Reference Manual and Guide

OTTER (Organized Techniques for Theorem-proving and Effective Research) is a resolution-style theorem-proving program for first-order logic with equality. OTTER includes the inference rules binary resolution, hyperresolution, UR-resolution, and binary paramodulation. Some of its other abilities and features are conversion from first-order formulas to clauses, forward and back subsumption, factoring, weighting, answer literals, term ordering, forward and back demodulation, evaluable functions and predicates, and Knuth-Bendix completion. OTTER is coded in C, is free, and is portable to many different kinds of computer.

Solution of the Robbins Problem

In this article we show that the three equations known as commutativity,associativity, and the Robbins equation are a basis for the variety ofBoolean algebras. The problem was posed by Herbert Robbins in the 1930s. Theproof was found automatically by EQP, a theorem-proving program forequational logic. We present the proof and the search strategies thatenabled the program to find the proof.

Experiments with discrimination-tree indexing and path indexing for term retrieval

This article addresses the problem of indexing and retrieving first-order predicate calculus terms in the context of automated deduction programs. The four retrieval operations of concern are to find variants, generalizations, instances, and terms that unify with a given term. Discrimination-tree indexing is reviewed, and several variations are presented. The path-indexing method is also reviewed. Experiments were conducted on large sets of terms to determine how the properties of the terms affect the performance of the two indexing methods. Results of the experiments are presented.

OTTER 3.3 reference manual.

OTTER is a resolution-style theorem-proving program for first-order logic with equality. OTTER includes the inference rules binary resolution, hyperresolution, UR-resolution, and binary paramodulation. Some of its other abilities and features are conversion from first-order formulas to clauses, forward and back subsumption, factoring, weighting, answer literals, term ordering, forward and back demodulation, evaluable functions and predicates, Knuth-Bendix completion, and the hints strategy. OTTER is coded in ANSI C, is free, and is portable to many different kinds of computer.

Mace4 reference manual and guide.

Mace4 is a program that searches for finite models of first-order formulas. For a given domain size, all instances of the formulas over the domain are constructed. The result is a set of ground clauses with equality. Then, a decision procedure based on ground equational rewriting is applied. If satisfiability is detected, one or more models are printed. Mace4 is a useful complement to first-order theorem provers, with the prover searching for proofs and Mace4 looking for countermodels, and it is useful for work on finite algebras. Mace4 performs better on equational problems than did our previous model-searching program Mace2.

Set theory in first-order logic: clauses for Go¨del's axioms

In this paper we present a set of clauses for set theory, thus developing a foundation for the expression of most theorems of mathematics in a form acceptable to a resolution-based automated theoren prover. Because Gödels formulation of set theory permits presentation in a finite number of first-orde formulas, we employ it rather than that of Zermelo-Fraenkel. We illustrate the expressive power of thi formulation by providing statements of some well-known open questions in number theory, and give some intuition about how the axioms are used by including some sample proofs. A small set of challeng problems is also given.

Otter - The CADE-13 Competition Incarnations

This article discusses the two incarnations of Otter entered in the CADE-13 Automated Theorem Proving System Competition. Also presented are some historical background, a summary of applications that have led to new results in mathematics and logic, and a general discussion of Otter.

COMPILING CONSTRAINT-CHECKING PROGRAMS FROM FIRST-ORDER FORMULAS

We describe a technique for extracting integrity tests from database constraints expressed as first-order formulas. The tests can be generated at database design time and are to be applied when updates to the database are issued. A significant feature is that the tests are to be applied before the update is made. The basic method is to assert a constraint for the current state of the database, express the new state in terms of both the old state and the general form of the update, deny that the constraint holds in the new state, and attempt to obtain a contradiction. When no contradiction is found, tests are to be extracted from the formulas generated and represent, in effect, a set of reasons why a contradiction could not be found, i.e., what extra conditions must be verified to guarantee the constraint in the new state. Some general results are given and open problems about the method are discussed.

Ivy: a preprocessor and proof checker for first-order logic

This case study shows how non-ACL2 programs can be combined with ACL2 functions in such a way that useful properties can be proved about the composite programs. Nothing is proved about the non-ACL2 programs Instead, the results of the non-ACL2 programs are checked at run time by ACL2 functions, and properties of these checker functions are proved. The application is resolution/paramodulation automated theorem proving for first-order logic. The top ACL2 function takes a conjecture, preprocesses the conjecture, and calls a non-ACL2 program to search for a proof or countermodel. If the non-ACL2 program succeeds, ACL2 functions check the proof or countermodel. The top ACL2 function is proved sound with respect to finite interpretations.

Experiments in Automated Deduction with Condensed Detachment

This paper contains the results of experiments with several search strategies on 112 problems involving condensed detachment. The problems are taken from nine different logic calculi: three versions of the two-valued sentential calculus, the many-valued sentential calculus, the implicational calculus, the equivalential calculus, the R calculus, the left group calculus, and the right group calculus. Each problem was given to the theorem prover Otter and was run with at least three strategies: (1) a basic strategy, (2) a strategy with a more refined method for selecting clauses on which to focus, and (3) a strategy that uses the refined selection mechanism and deletes deduced formulas according to some simple rules. Two new features of Otter are also presented: the refined method for selecting the next formula on which to focus, and a method for controlling memory usage.