Let \(G\) be a simple \(n\)-vertex graph and \(c\) be a colouring of \(E(G)\) with \(n\) colours, where each colour class has size at least \(2\). We prove that \(G\) contains a rainbow cycle of length at most \(\lceil \frac{n}{2} \rceil\), which is best possible. Our result settles a special case of a strengthening of the Caccetta-Häggkvist conjecture, due to Aharoni. We also show that the matroid generalization of our main result also holds for cographic matroids, but fails for binary matroids.
Today Tony will tell us about Transfinite Ford-Fulkerson on a Finite Network.