Resources for Yevamos daf 65
1. The משנה says that according to the חכמים a woman is not מצווה in פּריה ורביה. There is a large discussion as to whether a woman really has no obligation to get married and have children whatsoever or if she is just isn’t מצווה in פּרו ורבו but there is still some מצוה. תוספות in גיטין דף מ"א ד"ה לא תוהו says that while a woman is פּטור from פּרו ורבו she is חייבת in the מצוה of לשבת יצרה (which according to many means having one child). There is an interesting שיטה לא נודע למי in קידושין דף מ"א. The גמרא there says that there is a bigger מצוה for a woman to receive קידושין directly than to receive it from a שליח. The שיטה לא נודע למי asks that a woman has no מצוה to get married at all since she isn’t commanded in פּרו ורבו! He answers that while a woman doesn’t have the מצוה דאורייתא of פּרו ורבו, she does have a מצוה דרבנן. (Perhaps he is referring to the מצוה of שבת like תוספות). He then also suggests that she has a מצוה as an אינו מצווה ועושה. The ר"ן there says that while she doesn’t have her own מצוה,she has a מצוה of being מסייע he husband to do a מצוה. The מקנה there suggests that while she has no מצוה to go out and get married, if she wants to get married then she has a מצוה to get married since she will otherwise violate the לאו of לא תהיה קדשה.
2. The גמרא says that if a woman married three men and she couldn’t have children with all three, she still gets her כתובה from the first two husbands since she can claim that she just lost her ability to have children now and the first two marriages which resulted in no children were the fault of the first two husbands. The קובץ הערות in הוספות ב asks the seemingly obvious question: how can we just ignore the חזקה? The whole point of חזקה is to say that while after one or two times we can say it was just a fluke, after three times it is obvious that there is a pattern here and, for example, if the ox gored three times it is obvious that the ox wasn’t just having a bad day but that it is a dangerous ox. Or if a woman saw דם three times we assume she was always going to see at that time. So how can she claim that she just became an עקרה now? Why is this חזקה worse than all חזקות in ש"ס? He mentions that there is a חקירה about how חזקות work: do we say that after something occurs three times it proves to us that there is a pattern here that demonstrates that the subject always was this way, or is it that after three times a person has trained themselves to act a certain way and from now on they have a חזקה they will do it? He explains that while we can say a person’s body has been trained by ראית דם or by an ox goring, we cannot suggest that a woman trained herself to be barren! If so, this חזקה should have proven that she was always barren. The קהילת יעקב in נדה סימן נ"ו answers that a חזקה is not stronger than a רוב, and we never say חזקה ורוב are מוציא ממון. Therefore, where she is considered מוחזק she will win. (That would mean that when the גמרא says she can say "השתא הוא דכחשי", it just means she can say חזקה has no power here.) He also suggests that every woman stops being able to bare children at some point so it is reasonable to say השתא הוא דכחשי.
3. The גמרא says that it is מותר לשנות מפּני השלום. The ערוך לנר asks why the גמרא doesn’t say מותר לשקר מפּני השלום? He answers that one actually is not allowed to lie even מפּני השלום. One can only be "משנה" which is to say things in a way that can be misunderstood easily. He points out that this is also the משמעות of the ריטב"א here. Based on this, he explains that when the brothers said to יוסף via messengers “אביך צוה לפני מותו לאמר” that just meant “our father instructed his children before his death”. Then the messengers added their own thing that the brothers (not יעקב ) told them to say “כה תאמרו ליוסף".
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