This is referring to a case where one of the fathers comes with authorization to act on behalf of the other father to state his claim for him, and therefore the priest cannot reject his claim. But if they gave the money to two different priests an authorization is of no effect, as each priest can claim the other took the redemption money of the son who died.

The Gemara asks: But didn’t the Sages of Neharde’a say: We do not write an authorization document [adrakhta] concerning movable property? Therefore, in the case of redemption, where money, which has the status of movable property, is demanded from the priest, an authorization document may not be used. The Gemara answers: This statement, that one does not write authorization for movable property, applies only when the respondent, in this case the priest, already denied the claim against him. But in a case where the respondent did not yet deny the claim against him we write authorization even for movable property. In the case of redemption, although the priest claims the one issuing the claim against him is not the father of the son who died, he does not deny that he received the money.

§ The mishna teaches: With regard to two women who had not previously given birth who were married to two men, and gave birth to a male and a female who then became intermingled, the fathers are exempt from the mitzva of redemption but the son is obligated to redeem himself, as he certainly has firstborn status. If the offspring were two females and a male, or two males and two females, all of whom became intermingled, the priest has nothing here. Concerning this case Rav Huna teaches: If they gave birth to two males and a female the priest has nothing here, despite the fact that one of them is definitely a firstborn, as each father can claim that his firstborn is the female. In addition, the sons are exempt as well, since each can claim that the female was his sister and born first.

The Gemara asks: And with regard to the tanna of our mishna, why does he not state this case? The Gemara answers: Since you find this ruling that they are entirely exempt in a case where the women are married to two men, but you do not find it in a case of one man and two of his wives, as a firstborn was definitely born to that man and he must give five sela coins to a priest, the tanna does not teach the case of two women and two men either. The reason is that stylistically, the tanna prefers to teach the ruling: The priest has nothing here, only when the halakha is identical in a case of two wives of two men and a case of two wives of one man.

MISHNA: If the firstborn son dies within thirty days of birth, although the father gave five sela to the priest, the priest must return it. If the firstborn son dies after thirty days have passed, even if the father did not give five sela coins to the priest he must give it then. If the firstborn dies on the thirtieth day, that day’s halakhic status is like that of the day that preceded it, as the obligation takes effect only after thirty days have elapsed. Rabbi Akiva says: If the firstborn dies on the thirtieth day it is a case of uncertainty; therefore, if the father already gave the redemption payment to the priest he cannot take it back, but if he did not yet give payment he does not need to give it.

GEMARA: The Gemara asks: What is the reason of the Rabbis, i.e., the first tanna, who hold that the mitzva of redemption applies only after thirty days have elapsed? The Gemara explains that they derive the meaning of the term “month” stated in this context by means of a verbal analogy from the meaning of the term “month” stated in the context of the redemption of the Israelite firstborn in the wilderness via the Levites. Just as there, with regard to the redemption through the Levites, it is stated: “Number all the firstborn males of the children of Israel from a month old and upward” (Numbers 3:40), i.e., after thirty days, so too here, with regard to the mitzva of redemption for future generations, where it states: “From a month old you shall redeem” (Numbers 18:16), the requirement: And upward, applies as well, i.e., only after thirty days.

And Rabbi Akiva is uncertain in this regard, as one could claim: From the fact that it was necessary for the verse to write “and upward” with regard to the mitzva of valuations: “And if it be from sixty years old and upward” (Leviticus 27:7), and it is not derived from the redemption of the Israelite firstborns in the wilderness that the phrase “from…years old” means “and upward,” one can conclude the following: The redemption of the firstborn in the wilderness and valuations are two verses that come as one, i.e., to teach the same matter.

And there is a principle that any two verses that come as one do not teach their common halakha to other cases. If so, the halakha with regard to the mitzva of redeeming the firstborn for future generations would be that the thirtieth day is like the following day, which is not in accordance with the opinion of the Rabbis.

Or perhaps one could say: When do two verses that come as one not teach their common halakha? That is with regard to general halakhot, i.e., entirely different areas of halakha. But with regard to themselves, i.e., similar cases, they do teach. If so, one should derive permanent halakha of redemption of firstborns from the redemption of the firstborn in the wilderness. And it is due to that reason that Rabbi Akiva is uncertain concerning a firstborn on his thirtieth day.

Rav Ashi says: All concede with regard to mourning that the thirtieth day is like the preceding day, i.e., if the son died on the thirtieth day it is considered as though he died on the day before and he has the status of a stillborn, and the rites of mourning are not observed. And the reason is as Shmuel says: The halakha is in accordance with the statement of the more lenient authority in matters relating to mourning.

MISHNA: If the father of the firstborn dies within thirty days of birth the presumptive status of the son is that he was not redeemed, until the son will bring proof that he was redeemed. If the father dies after thirty days have passed the presumptive status of the son is that he was redeemed, until people will tell him that he was not redeemed. If one had both himself to redeem and his son to redeem, his own redemption takes precedence over that of his son. Rabbi Yehuda says: The redemption of his son takes precedence, as the mitzva to redeem the father is incumbent upon his own father, and the mitzva to redeem his son is incumbent upon him.

GEMARA: It was stated: In the case of one who redeems his firstborn son within thirty days of his birth by giving a priest five sela coins, Rav says his son is redeemed and Shmuel says his son is not redeemed. The Gemara explains: Everyone agrees that if the father said: He is redeemed from now, that his son is not redeemed, as the obligation to redeem the son is not yet in effect. Likewise, if the father says the redemption should take effect after thirty days, and the money is still there, in the possession of the priest, after thirty days, his son is certainly redeemed, as the money is in the priest’s possession when the obligation of redemption comes into effect.

They disagree in a situation where the father says the redemption should take effect after thirty days but the money was squandered away in the meantime. Rav says his son is redeemed, just as is the halakha with regard to the betrothal of a woman on the condition that it takes effect after thirty days. In that case there, is it not correct that even though the money was squandered away during the thirty days it is a valid betrothal?