An old oven was within a new [oven] and there was a sereedah over the mouth of the old [oven]: [If] the old [oven] is removed and the sereedah would fall, [then] everything is tamei, but if not, everything is tahor. A new [oven] was within an old [oven] and there was a sereedah over the mouth of the old [oven]: If there is less than a handbreadth between the new [oven] and the sereedah, [then] everything within the new [oven] is tahor.