Consider, for example, the construction of the free group in two generators. One starts with an alphabet consisting of the five letters formula_2. In the first step, there is not yet any assigned meaning to the "letters" formula_3 or formula_4; these will be given later, in the second step. Thus, one could equally well start with the alphabet in five letters that is formula_5. In this example, the set of all words or strings formula_6 will include strings such as "aebecede" and "abdc", and so on, of arbitrary finite length, with the letters arranged in every possible order.