Unambiguous DNFs and Alon-Saks-Seymour

Kaspars Balodis, Shalev Ben-David, Mika Göös, Siddhartha Jain, Robin Kothari

Abstract: We exhibit an unambiguous $k$ -DNF formula that requires CNF width $\tilde\Omega(k^{2})$ , which is optimal up to logarithmic factors. As a consequence, we get a near-optimal solution to the Alon–Saks–Seymour problem in graph theory (posed in 1991), which asks: How large a gap can there be between the chromatic number of a graph and its biclique partition number? Our result is also known to imply several other improved separations in query and communication complexity.