The ham sandwich theorem
states that it is possible to
divide a sandwich made up of three layers (ham, butter, bread)
exactly in half with just one cut of the knife. Here's the mathematical
Theorem Given three bounded subsets of R3 there exists
a plane in R3 dividing each of the subsets in half
The proof of the ham sandwich theorem
is a corollary of the Borsuk-Ulam theorem.