Write a regular expression that captures the set of strings composed of 'a', 'b', and 'c', where any string uses at most two of the three letters (for example, "abbab" is a valid string, or "bccbb", or "ccacaa", but not "abccba": strings that contain only one of the three letters are also fine). Give a non-deterministic finite automaton that captures the regular expression from Using the construction described in class, give a deterministic version of the automaton. Repeat the previous three steps for strings composed of 'a', 'b', 'c', and 'd', where any string uses at most three of the four letters