Oh, I see now! I'm not a mathematician, therefore, I can't grasp the concept fully. First of all, it does not need to become zero for the problem to exist. Secondly, the key point is "approach zero". I shall now use the same intonation as your post above: I realize this is tricky for you to grasp, therefore, I suggest that instead of trying to sideline the argument into whether the supply will reach zero or some quantity that is not exactly zero, which is a wrong assumption on your part anyway, that you reconsider the real premise put forth in this thread, and find a means to object to it, instead.  That is, if it's not too tricky for you.