A Subatomic Proof System for Decision Trees

Chris Barrett, Alessio Guglielmi

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Abstract

We design a proof system for propositional classical logic that integrates two languages for Boolean functions: standard conjunction-disjunction-negation and binary decision trees. We give two reasons to do so. The first is proof-theoretical naturalness: the system consists of all and only the inference rules generated by the single, simple, linear scheme of the recently introduced subatomic logic. Thanks to this regularity, cuts are eliminated via a natural construction. The second reason is that the system generates efficient proofs. Indeed, we show that a certain class of tautologies due to Statman, which cannot have better than exponential cut-free proofs in the sequent calculus, have polynomial cut-free proofs in our system. We achieve this by using the same construction that we use for cut elimination. In summary, by expanding the language of propositional logic, we make its proof theory more regular and generate more proofs, some of which are very efficient.

That design is made possible by considering atoms as superpositions of their truth values, which are connected by self-dual, non-commutative connectives. A proof can then be projected via each atom into two proofs, one for each truth value, without a need for cuts. Those projections are semantically natural and are at the heart of the constructions in this paper. To accommodate self-dual non-commutativity, we compose proofs in deep inference.
Original languageEnglish
Article number26
Pages (from-to)1-25
JournalACM Transactions on Computational Logic
Volume23
Issue number4
Early online date28 Jun 2022
DOIs
Publication statusPublished - 31 Oct 2022

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