Discrepancy after adding a single set (Q2568502)

It is shown that the hereditary discrepancy of a hypergraph \(\mathcal F\) on \(n\) points increases by a factor of at most \(O(\log n)\) when one adds a new edge to \(\mathcal F\). The proof is short, illustrative and elegant. It remains open whether this factor can be improved to \(O(1)\).