A compact representation of proofs

Studia Logica 46 (4):347 - 370 (1987)
A structure which generalizes formulas by including substitution terms is used to represent proofs in classical logic. These structures, called expansion trees, can be most easily understood as describing a tautologous substitution instance of a theorem. They also provide a computationally useful representation of classical proofs as first-class values. As values they are compact and can easily be manipulated and transformed. For example, we present an explicit transformations between expansion tree proofs and cut-free sequential proofs. A theorem prover which represents proofs using expansion trees can use this transformation to present its proofs in more human-readable form. Also a very simple computation on expansion trees can transform them into Craig-style linear reasoning and into interpolants when they exist. We have chosen a sublogic of the Simple Theory of Types for our classical logic because it elegantly represents substitutions at all finite types through the use of the typed -calculus. Since all the proof-theoretic results we shall study depend heavily on properties of substitutions, using this logic has allowed us to strengthen and extend prior results: we are able to prove a strengthen form of the firstorder interpolation theorem as well as provide a correct description of Skolem functions and the Herbrand Universe. The latter are not straightforward generalization of their first-order definitions.
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DOI 10.1007/BF00370646
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References found in this work BETA
Raymond M. Smullyan (1968). First-Order Logic. New York [Etc.]Springer-Verlag.
Dag Prawitz (1968). Hauptsatz for Higher Order Logic. Journal of Symbolic Logic 33 (3):452-457.

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Citations of this work BETA
Willem Heijltjes (2010). Classical Proof Forestry. Annals of Pure and Applied Logic 161 (11):1346-1366.
Stefan Hetzl (2010). On the Form of Witness Terms. Archive for Mathematical Logic 49 (5):529-554.

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