Let G$G$ be a multipartite graph on r$r$ classes, each containing k$k$ vertices, such that there is no independent set which contains at least one vertex from each class. I believe such graphs contain a complete bipartite graph $K_{f(k),f(k)}$ for each fixed r$r$, with f$f$ an increasing (possibly even linear) function, but the proof eludes me so far. Google search led me to extremely results about Ramsey-type results for bipartite subgraphs, but not complete ones. Any insights are much appreciated.