Dominator Trees and Fast Verification of Proof Nets

We consider the following decision problems: PROOFNET : Given a multiplicative linear logic (MLL) proof structure, is it a proof net? ESSNET : Given an essential net (of an intuitionistic MLL sequent), is it correct? In this paper we show that linear-time algorithms for ESSNET can be obtained by constructing the dominator tree of the input essential net. As a corollary, by showing that PROOFNET is linear-time reducible to ESSNET (by the trip translation), we obtain a linear-time algorithm for PROOFNET. We show further that these linear-time algorithms can be optimized to simple one-pass algorithms – each node of the input structure is visited at most once. As another application of dominator trees, we obtain lineartime algorithms for sequentializing proof nets (i.e. given a proof net, find a derivation for the underlying MLL sequent) and essential nets.