No, because you will still need to apply a special case to stop the recursion of putting a period after a period forever. If a sentence ends in a period then what ends the expression that contains the sentence and the period? Answer: another period because you can think of that expression as a sentence too. So you need a special case that says if there are going to be two periods next to each other then terminate the recursion. Similarly your .". asinine suggestion fails since it implicitly invokes a special rule, but is worse than the elegant special rule of just having one period.