Tree-like resolution is superpolynomially slower than dag-like resolution for the pigeonhole principle

Abstract

Our main result shows that a shortest proof size of tree-like resolution for the pigeonhole principle is superpolynomially larger than that of DAG-like resolution. In the proof of a lower bound, we exploit a relationship between tree-like resolution and backtracking, which has long been recognized in this field but not been used before to give explicit results.