Two stones were made into a stove and became tamei, [and then] one placed a stone next to [one of the tamei stones] on one side, and a stone next to [the other tamei stone] on the other side: Half of [one tamei stone] is tamei and half of it is tahor, and half of [the other tamei stone] is tamei and half of it is tahor. [If] the tahor [stones] were removed, the others return to their state of tumah.