First-order proofs without syntax
Abstract
Proofs are traditionally syntactic, inductively generated objects. This paper reformulates first-order logic (predicate calculus) with proofs which are graph-theoretic rather than syntactic. It defines a combinatorial proof of a formula φ as a lax fibration over a graph associated with φ. The main theorem is soundness and completeness: a formula is a valid if and only if it has a combinatorial proof.
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