פירוש על קידושין 32:5

We might have thought to say that R. Shimon taught “signs” because they have a lower amount, as we learned yesterday from R. Safra. But the problem is that the death of the master is assumed to be one of these “four ways” and yet it too does not have a fixed time.
The Talmud responds by saying the death of the master is also not taught.