Professor Rodl, one of my PhD advisors, is in town for a week. So while most of the department is off at some cabin somewhere for a clinic on Ergodic Ramsey Theory, I stay in Prague.

We both have other work to do, but have a problem to work on together, so meet frequently through the week. We run into troubles, but Rodl impresses me again with how clever he is.

"You think that's clever?" he says. He reaches up pulls out a 50 crown piece from behind my ear.