Razborov Disjointness Lower Bound , Forster ’ S Theorem

In this lecture, we show two results dealing with lower bounds in communication complexity. The first lower bound is an Ω(n) lower bound on the distributional complexity of Disjointness due to [3, 8]. Here we will present the simplified proof presented in [8]. In the second part, we will show how to obtain lower bounds on the unbounded error probabilistic communication complexity by Forster’s method [2] of lower-bounding the sign rank of the corresponding matrix by showing that it has a small spectral norm.