Their quest started in 1994, when Deiermann showed Mabry a revised version of the pizza problem, again published in Mathematics Magazine (vol 67, p 304). Readers were invited to prove two specific cases of the pizza theorem. First, that if a pizza is cut three times (into six slices), the person who eats the slice containing the pizza's centre eats more. Second, that if the pizza is cut five times (making 10 slices), the opposite is true and the person who eats the centre eats less.
Only the first statement was proven. Deiermann and Mabry worked on proving the second off and on until their breakthrough in 2006. Now that they have proven the theorem, they are working on other problem, such as how to divide a calzone. Link -via Metafilter
(image credit: Flickr user zharth)