Unification nets
Dominic J. D. Hughes · 2018
Proof nets for MLL (unit-free Multiplicative Linear Logic) are concise graphical representations of proofs which are canonical in the sense that they abstract away syntactic redundancy such as the order of non-interacting rules. We argue that Girard's extension to MLL1 (first-order MLL) fails to be canonical because of redundant existential witnesses, and present canonical MLL1 proof nets called unification nets without them. For example, while there are infinitely many cut-free Girard nets ∀x Px ⊢ ∃x Px, one per arbitrary witness for ∃x, there is a unique cut-free unification net, with no specified witness.