The boolean isomorphism problem

Abstract

We investigate the computational complexity of the Boolean isomorphism problem (BI): on input of two Boolean formulas F and G decide whether there exists a permutation of the variables of G such that F and G become equivalent. Our main result is a one-round interactive proof for BI, where the verifier has access to an NP oracle. To obtain this, we use a recent result from learning theory by N. Bshouty et al. (1995), that Boolean formulas can be learned probabilistically with equivalence queries and access to an NP oracle. As a consequence, BI cannot be Σ₂p complete unless the polynomial hierarchy collapses. This solves an open problem posed previously. Further properties of BI are shown: BI has And- and Or-functions, the counting version, BI, can be computed in polynomial time relative to BI, and BI is self-reducible.