@Article{RWY03,
author={Alexander Razborov and Avi Wigderson and Andrew Yao},
title={Read-once Branching Programs, Rectangular Proofs of the
Pigeonhole Principle adn the Transversal Calculus},
journal={Combinatorica},
volume={22},
number={4},
pages={555-574},
year={2003},
}