More a question to some conceptual understanding of combinatorics. The number of ways of picking Na elements to be in a box A, Nb to be in a box B and Nc to be in box C is given by: N!/(Na!Nb!Nc!) One can proof this by saying: Suppose we start by putting Na in box A and so on. Now I have always wondered why on a deeper level you get the same result no matter on which box you start to put in your elements. Do all physical systems obey this kind of counting logic? Edit: hmm.. maybe this is all gibberish..