Assume that for all grammars, the alphabet set is E(sigma) =  {a,b}, the starting variable is S, all upper case symbols represents variables. For each given production rule,
	- Enumerate all the strings of length 4 or less it can produce.
	- Give a verbal description of the language it generates.
	- Generalize the yielded language into its set notation as concise as possible.

S->aS|λ