(Mishnah): To take money from the giver, one must bring proof.
(R. Yochanan): The recipient must bring witnesses (that the giver was healthy when he gave the gift).
(Reish Lakish): He must validate the document.
Question (R. Yochanan - Beraisa): It occurred that Reuven sold property, then died. His heirs said that the sale was invalid, for he was a minor at the time. They (the buyers) asked to check the body (for Simanim of adulthood).
R. Akiva: Firstly, you may not check the body, for it is a disgrace. Secondly, Simanim often change after death.
Answer (Reish Lakish): No, the buyers were Muchzak in the property. His heirs wanted to check the body (to prove that he was a minor) to take back the property.
Nidah 46a (Rava): A girl may do Mi'un anytime until 12 full years. After 12, she may not do Mi'un or Chalitzah.
Question: He forbids Mi'un, for he assumes that she is an adult (and the marriage became mid'Oraisa). If she is an adult, she may do Chalitzah!
Rava is not in Safek whether she is an adult, for he taught that we need not check a girl above 12. She is Muchzekes to be an adult.
Answer #1: Normally, we assume that she is an adult. She may not do Chalitzah in a case when we see that she does not have hairs now. She may not do Mi'un, lest she brought hairs after 12 years, and they fell out.
Question: This is according to the opinion that is concerned that they fell out. According to the opinion that is not concerned, how can we answer?
Answer #2: We did not check her. Regarding Chalitzah we are concerned (lest she is still a minor). Rava's Chazakah refers to Mi'un (we are stringent not to allow Mi'un). She may not do Chalitzah until we see hairs.
46b: If a Mufla Samuch l'Ish (a minor shortly before adulthood) was Makdish something and an adult ate it, he is lashed.
46b: This is like R. Yochanan and Reish Lakish, who say that adults are lashed for (benefit from) a minor's Hekdesh. Rav Kahana exempts
Rambam (Hilchos Ishus 2:15): If a boy above 13 did not bring a Siman below, and he brought all the Simanim above, it is a Safek whether he is a minor of adult. If he was not checked below, since he has Simanei Bagrus above, he is assumed to be an adult.
Tosfos (154a DH Simanim): Why do we assume that he was a minor after 13 years? In Nidah we say that she need not be checked, for there is a Chazakah that she brought Simanim! We can say that the seller did not have Simanim after 13 years, therefore, there is a Safek.
Shulchan Aruch (CM 35:1): A minor cannot testify until he brings two hairs after 13 years. If he was not checked until long after 13 years, and he had two hairs, he is Muchzak to be an adult from 13 years.
Shev Shematsa (5:11-13): Bava Basra 154 connotes that Chazakah d'Rava is merely a stringency. One is lashed for benefit from something forbidden by a vow of a Mufla Samuch l'Ish. The Rambam holds that this is a boy or girl after 13 or 12 years, without hairs. The Torah did not require hairs for vows. Rashi and Tosfos hold that it is a year before adulthood. How can one be lashed for the vow? The warning is Safek, for perhaps he will not bring hairs within a year! They must hold that Chazakah d'Rava is Vadai. However, if he did not bring hairs within a year, retroactively we know that it was not a vow. Tosfos (154a DH Simanim) says that if one did not bring hairs right after 13 years, Chazakah d'Rava does not apply. If so, he is not a Mufla Samuch l'Ish, for there is no Chazakah that he will bring hairs within a year! In Nidah we say that she need not be checked, for there is a Chazakah that she brought Simanim! We can say that the seller did not have Simanim after 13 years, therefore, there is a Safek.
Avnei Nezer (EH 215:17): Chazakah d'Rava is even to be lenient. Chachamim were stringent to check for Chalitzah. Do not say that CM 35 discusses testimony to keep money, and as long as the witnesses were not checked, their testimony is void. Tosfos (Bava Kama 72b) says that even Rav Chisda, who says 'what good are Safek Pasul witnesses?!' agrees that their testimony enables one to avoid paying. The same applies to a Safek minor. Rather, CM 35 discusses testimony to obligate one to pay. Therefore, we do not rely on Chazakah d'Rava, which is based on a majority, for we do not rely on the majority for monetary matters.
Noda b'Yehudah (1 EH 61): Why did Rava need to say that a girl cannot do Mi'un after 12 years due to a Chazakah? It would have sufficed to say that perhaps she brought two hairs! The Gemara said that Rava forbids Chalitzah in a case when we see that she does not have hairs now, and he forbids Mi'un, lest she brought hairs after 12 years, and they fell out. To answer for the opinion that is not concerned lest hairs fell out, we needed to say that he is stringent about Chalitzah. The Halachah is, we are concerned lest they fell out, so we can explain simply that we checked her and did not find hairs. Tosfos (154a) asked why we don't apply Chazakah d'Rava against Chezkas Mamon. We find that we do not apply it even for Chalitzah! Rather, we must say like I said, that it applies even to Chalitzah. Mi'un is forbidden due to concern lest the hairs fell out, like we initially answered. Tosfos answered that the case is, the seller did not have Simanim after 13 years, therefore, it was a Safek. Reish Lakish said that validating the document suffices to extract money, i.e. due to the Chazakah that witnesses sign only if the parties are adults. Perhaps the witnesses relied on Chazakah d'Rava, and assumed that the giver brought hairs! If Chazakah d'Rava suffices to extract money, all the more so witnesses may rely on it to sign! Perhaps the witnesses did not know that the giver had been checked after 13 years and no hairs were found! I say that Chazakah d'Rava is strong enough to transfer money, but when it is possible to check, we check, e.g. for Chalitzah. Since the giver was checked after 13 and no hairs were found, it was a Safek about the time of the gift, and after death it was impossible to check. The witnesses were not allowed to rely on the Chazakah, for then it was possible to check. Tosfos holds that we can transfer money due to Chazakah d'Rava if the giver died and we cannot check. No Posek explicitly disagrees, so we rely on this. This shows that Chazakah d'Rava is stronger than a majority (which does not help to transfer money); a regular Chazakah is weaker than a majority. Why must we check? We rely on a majority and need not check the 18 Tereifos! Regarding checking, we distinguish between permitting what was established to be Asur (e.g. for a Yevamah to marry a stranger, and until now she or the Yavam was a minor). However, the Rosh (33:5) argues. He says that Simanim show that the youth was an adult retroactively from 13. The Rosh did not say so in a case when he was checked after 13 and found not to have Simanim. If much later he was found to have Simanim, we cannot retroactively make him an adult. From which time could we say that he brought Simanim? The time between the Bedikos is a Safek. Since the Rosh holds that he was not checked in between, Tosfos' question return: Chazakah d'Rava should say that he was an adult! Rather, the Rosh must hold that Chazakah d'Rava is only a stringency. We do not rely on it for Chalitzah at all, and all the more so to extract money. The Shulchan Aruch (CM 35) rules like the Rosh, but the Ramban disagrees. He proves that the youth died right after selling, for if not, Bedikah afterwards would not prove that he was an adult when he sold. The Beis Yosef (EH Sof 43 DH v'Chosav) says that the Rashba disagrees with the Rosh. This is a printing mistake; it should say 'Ramban'. However, perhaps the Ramban agrees with the Rosh's law, and also holds like Tosfos! I.e. if we cannot check, we transfer money due to Chazakah d'Rava. However, in Bava Basra the boy was checked a while before he sold and did not have hairs, therefore, checking afterwards would not establish him to be an adult retroactively, like the Shulchan Aruch's ruling.
Noda b'Yehudah (ibid.): Tosfos concluded that Chazakah d'Rava is not just a stringency. Perhaps he learns from the word 'Chazakah' (Rava did not just say that we are concerned). Or, since we rule that we are concerned lest hairs fell out, we need not say that Mi'un is a mere stringency. Rather, letter of the law we assume that she brought hairs. Rava's Chidush was about Mi'un, and not that we must check for Chalitzah. This explains why he discusses a girl. Chachamim normally discuss men. The Chidush about Chalitzah could have been taught regarding a Yavam! Rather, his primary Chidush was for Mi'un, which is only for a girl. However, perhaps he preferred to teach about a girl, for even though she brings Simanim earlier (12 years), we assume that she brought them right away. A Yevamah came in front of Rebbi, and he ordered to check her (Yevamos 105b) The Gemara connotes that she had not been checked yet. The one who says that Rava requires checking for Chalitzah only if she was found not to have hairs after 12 years must say that Rava argues with Rebbi.
Yabi'a Omer (7 OC 46): The Ramban (Chulin 3b) and Rashba (3a) hold that Chazakah d'Rava is a proper Chazakah, just when possible we must verify it. The Rivash (182) agrees, for we rely on it to believe women about Simanim (Nidah 46b). The Maharit (1:41,51) explains that this is due to the Chazakah; the women merely reveal a matter (that the Chazakah was fulfilled).