Imagine we have a new programming language with identifiers that is made up from letter and digits But in an unusual way a) where the identifier must have at least one letter, but it need not be the first character. e.g. a21, a, 2a, 321a, a321 but not 321 b) where the identifier must have at least one letter and there must be at least one digit before the leftmost letter. e.g. 321a, 3a21, 321abc but not a2i (no digits left of a)