GUILD OF MATHEMATICIANS
WARNING: THIS GUILD IS HIGHLY NON-CANONICAL.
IT IS NOT MENTIONED IN ANY DISCWORLD BOOK.
IT WAS MENTIONED AT THE 2006 DISCWORLD CONVENTION, MIND YOU.
BUT THAT WAS BY ME.
A shield quartered with, on the upper left quarter, a sum chalke on a board sable. On the upper right quarter, a cylinder with sphere inscripté on a field azure. On the lower left quarter, an unknown rampant upon a finite field gules. On the lower right quarter, a repetition fractally of the whole.
The motto translates as "The proof is left as an exercise for the reader".