Rabbi Yitzchak enters the debate about burning Passover leftovers with yet another angle of attack, proving the same conclusion through a different logical comparison. His argument centers on chametz — leavened bread — and its relationship to the Pesach (Passover) leftovers.
The reasoning is sharp. Chametz has an extraordinarily strict legal status. The Torah forbids not just eating it during Passover but even possessing it. You may not see it in your domain. You may not find it in your house. The prohibitions of "being seen" and "being found" (Exodus 12:19, 13:7) make chametz uniquely severe among Passover restrictions. And yet, despite this extreme severity, the burning of chametz does not override the festival. You must destroy your chametz before the holiday begins, not during it.
Now consider the Passover leftovers. Their legal status is far less severe than chametz. There is no prohibition against possessing them — only against eating them past the deadline. If the more severely prohibited chametz cannot be burned on the festival, then surely the less severely prohibited leftovers cannot be burned on the festival either. The kal va'chomer is airtight.
Rabbi Yitzchak's contribution completes a triple proof. Rabbi Yishmael argued from the general prohibition of labor on festivals. Rabbi Yonathan argued from the relationship between Shabbat (the Sabbath) and festival permissions. Rabbi Yitzchak argues from the precedent of chametz. Three sages, three independent logical paths, one conclusion — and all three agree that the repeated "until morning" in the Torah must teach something else entirely, since the burning prohibition needs no verse to establish it.