Strange - I was just searching for 'Riemann' - trying to find out if their suncream is really worth the extra £.
If you mean that P20 stuff, it's great. Slosh it on in the morning and that's it for the day. Sweating, swimming, washing, whatever - doesn't have any effect on it. I swear by it.
If you mean the hypothesis, that's pretty good too. I got mine back in, ooh, 1982, and it's still going strong. Attempts to prove, disprove, whatever - no effect at all so far