[If] four brothers were married to four women and [then] died, if the eldest of them wished to perform yibum with all of them, he may do so.  [If] someone was married to two women and [then] died, conjugal relations or chalitzah with one of them releases her co-wife. [If] one was qualified and one was disqualified, if he is [going] to perform chalitzah, he should do so with the disqualified one; but if he is [going] to perform yibum, he may do so with the qualified one.

[If] one remarries his divorced wife, or he marries his chalutzah, or the relative of his chalutzah, he must send her away, and the child [of that union] is a mamzer; [these are] the words of R' Akiva. The Sages, however, say: The child is not a mamzer. But they admit that if he marries the relative of his divorced wife, that the child is a mamzer.