What does it mean "regular" functions? Functions that has a lot of fiber? Or functions like + - * /?
My own question. These puzzles that ask to express something in terms of something can they be solved by Galois theory? Becuase what we are really cosidering is are all the premutations, which is similar to the classical approach of solution by radicals, by looking at all the premutations. Anybody have any idea?