Yevamot 55 - First Day of Rosh Chodesh Iyar, May 1, 30 Nissan

Today's daf is sponsored by Rochelle Cheifetz in honor of her mother, Chana Cohen, Chana bat Rav Moshe and Tzipora Mashbaum, on her first yahrzeit. "It is still hard to believe that my wonderful and beautiful mother is no longer here to fill her role as matron of our extended family. She dedicated herself to family and Israel. Her beautiful and warm smile, exuberance and guidance are strongly missed." Today's daf is sponsored by Adi Levi Eitan for a refuah shleima for Chana Sara bat Esther.  The forbidden relationship of one's wife's sister applies to her sister from either her mother or her father. From where is this derived? After unsuccessfully attempting to learn it from one's sister (both) or one's aunt (only if the father and his brother share the same father), it is successfully derived from one's brother's wife who is forbidden both through the mother and the father. From where do we know that one's brother's wife is a brother from either side? It is derived from extra words in Vayikra 18:16. The Gemara suggests other possible derivations from the extra words in the verse, but in the end, conclude that all those can be learned from other verses and therefore this one is used to teach from the mother and the father. If so, why don't we say that yibum applies also to a brother from the mother? A series of drashot on verses from the section of forbidden relationships are brought. Why is karet mentioned by one's sister (Yayikra 20:17)  when it could have been derived from the concluding verse in that section? Rabbi Yochanan holds that it teaches that if you performed several forbidden actions with people who were forbidden to you without realizing that it was forbidden, you would be liable to bring a separate sin offering for each one. Rabbi Yitzchak learns that you get karet but not lashes, even if you were warned that you would receive lashes. He derives separate sin offerings from the verse about nidda. Why does one verse say "you will be childless" and another says "you will die childless"? Each refers to a different situation - where you had children previously or you did not have children. Why are both needed? From where do we derive that for violating negative prohibitions involving forbidden relationships, negative prohibitions regarding relationships with kohanim and for violating positive commandments, if one engaged in the initial stages of intercourse, one would be liable? How do we know that initial stages of intercourse can be effective in performing the mitzva of yibum or kiddushin (some think it is referring to marriage)? Why is the term "shichvat zera," cohabitation with seed, mentioned by a designated maidservant, a married woman, and a sotah? Each one comes to exclude a particular case. What is the definition of haaraah, the initial stages of intercourse? Different opinions are brought.