• This really existing plate shows that the german word "Funktor" (functor) has a meaning in the real world, something like a remotely ("Funk") operated gate ("Tor"). It recommends to stay 2 meters away...

  • Original soundtrack of David Hilbert speaking about "Naturerkennen und Logik" (in german)

  • With this shocking application of the fundamental group it is demonstrated that clipping two carabinders together can have an unexpected effect.
  • Here one can play games like chess or tic-tac-toe on closed surfaces like the Klein bottle.
  • It is shown how to slice a bagel into two linked halves.

  • The picture shows a proof that 31.5 = 32.5.

  • Below is a picture of a commutative diagram that I have found on a hiking trail near Berkeley.