Amelia Harrison

On Equivalence of Infinitary Formulas under the Stable Model Semantics

Propositional formulas that are equivalent in intuitionistic logic, or in its extension known as the logic of here-and-there, have the same stable models. We extend this theorem to propositional formulas with infinitely long conjunctions and disjunctions and show how to apply this generalization to proving properties of aggregates in answer set programming.

Infinitary Equilibrium Logic and Strong Equivalence

Strong equivalence of logic programs is an important concept in the theory of answer set programming. Equilibrium logic was used to show that propositional formulas are strongly equivalent if and only if they are equivalent in the logic of here-and-there. We extend equilibrium logic to formulas with infinitely long conjunctions and disjunctions, define and axiomatize an infinitary counterpart to the logic of here-and-there, and show that the theorem on strong equivalence holds in the infinitary case as well.

Infinitary equilibrium logic and strongly equivalent logic programs

Abstract Strong equivalence is an important concept in the theory of answer set programming. Informally speaking, two sets of rules are strongly equivalent if they have the same meaning in any context. Equilibrium logic was used to prove that sets of rules expressed as propositional formulas are strongly equivalent if and only if they are equivalent in the logic of here-and-there. We extend this line of work to formulas with infinitely long conjunctions and disjunctions, show that the infinitary logic of here-and-there characterizes strong equivalence of infinitary formulas, and give an axiomatization of that logic. This is useful because of the relationship between infinitary formulas and logic programs with local variables.

On Equivalent Transformations of Infinitary Formulas under the Stable Model Semantics

It has been known for a long time that intuitionistically equivalent formulas have the same stable models. We extend this theorem to propositional formulas with infinitely long conjunctions and disjunctions and show how to apply this generalization to proving properties of aggregates in answer set programming.

Proving infinitary formulas

The infinitary propositional logic of here-and-there is important for the theory of answer set programming in view of its relation to strongly equivalent transformations of logic programs. We know a formal system axiomatizing this logic exists, but a proof in that system may include infinitely many formulas. In this note we describe a relationship between the validity of infinitary formulas in the logic of here-and-there and the provability of formulas in some finite deductive systems. This relationship allows us to use finite proofs to justify the validity of infinitary formulas. This note is under consideration for publication in Theory and Practice of Logic Programming.

First-Order Modular Logic Programs and their Conservative Extensions (Extended Abstract)

Modular logic programs provide a way of viewing logic programs as consisting of many independent, meaningful modules. This paper introduces first-order modular logic programs, which can capture the meaning of many answer set programs. We also introduce conservative extensions of such programs. This concept helps to identify strong relationships between modular programs as well as between traditional programs. We show how the notion of a conservative extension can be used to justify the common projection rewriting. This note is under consideration for publication in Theory and Practice of Logic Programming.

Stable models for infinitary formulas with extensional atoms

The definition of stable models for propositional formulas with infinite conjunctions and disjunctions can be used to describe the semantics of answer set programming languages. In this note, we enhance that definition by introducing a distinction between intensional and extensional atoms. The symmetric splitting theorem for first-order formulas is then extended to infinitary formulas and used to reason about infinitary definitions. This note is under consideration for publication in Theory and Practice of Logic Programming.

First-Order Modular Logic Programs and their Conservative Extensions

Modular logic programs provide a way of viewing logic programs as consisting of many independent, meaningful modules. This paper introduces first-order modular logic programs, which can capture the meaning of many answer set programs. We also introduce conservative extensions of such programs. This concept helps to identify strong relationships between modular programs as well as between traditional programs. We show how the notion of a conservative extension can be used to justify the common projection rewriting. This note is under consideration for publication in Theory and Practice of Logic Programming.

Formal Methods for Answer Set Programming

Answer set programming is a logic programming paradigm that has increased in popularity over the past decade and found applications in a wide variety of elds. Even so, manuals written by the designers of answer set solvers usually described the semantics of the input languages of their systems using examples and informal comments that appeal to the users’ intuition, without references to any precise semantics. We describe a precise semantics for the input language of the grounder gringo, which serves as the front end for several answer set solvers. The semantics represents gringo rules as innitary propositional formulas. We develop methods for using this semantics to prove properties of gringo programs, such as verifying program correctness.