The disagreements between Abaye and Rava are amongst the most important in the Gemara. The halakhah always follows Rava's opinion, with only six exceptions, where the halakhah follows Abaye’s opinion. Those six are referred to by the Gemara by the acronym – YA”L KG”M (יע"ל קג"ם):
- When a person does not realize that he has lost an object until after it is picked up by someone else, and he gives up ownership when he realizes it, can we apply it retroactively? בבא מציעא כא. יֵּ אוּש שלא מדעת
- When witnesses are found to be unreliable, does their status change as of that time or from the time that their false testimony was made? סנהדרין כז. עַ ד זוֹמֵם
- When a pole is standing on its own (it was not placed there by a person), can it be used as part of the structure that will create a legal private domain on Shabbat for the purpose of carrying? ערובין טו. ל חִּי ה עוֹמֵד מֵאֵל יו
- Does the days of the tumah period following childbirth count towards the seven clean days for a zivah? נידה לז . אין לידה סותרת בזיבה
- When a person is not able to prevent benefit from a prohibited item, is it permitted when one does not intend to benefit? פסחים כה: לא אפשר ולא מתכוין
- If a couple gets married, but will be unable to consummate their marriage, does it have legal significance? קדושין נא. קִ דוּשִּין ש לֹא נִּמְסְר וּ לְבִּיא ה
- If a person makes a statement that can be understood as affecting the divorce that has been sent to his wife, must we take it into consideration when ruling on the validity of the divorce? גיטן לד. גִּלוּי דַעְת א בְגִּיט א
- Can a person who commits sins be trusted to testify in court? סנהדרין כז. מוּמ ר אוֹכֵל נְבִּלוֹת להַכְעִּיס
However, the order in this acronym is not according to the order that one finds these 6 places in Shas. (Lechi is the first found in Shas but only listed third, FalsE Witnesses is found listed prior to Kiddushin and Gitin.)
The Noda BiYehudah addresses this issue in his first published book, Derush Lezion. In the year 1751 his sermon asked the above question. For the next three years he delivered sermons explaining the answer to this question citing references throughout Shas to show that this was the proper order.
It is possible that he discussed this topic on the Shabbos of Tesuvah to emphasize that Teshuvah needs to be based on study and cleaving to Torah learning as the verse states, “Return us our Father to Your Torah and bring us close, our King, to Your service.”
Yechezkel ben Yehuda Landau (8 October 1713 – 29 April 1793)
Yechezkel ben Yehuda Landau was an influential authority in halakha (Jewish law). He is best known for the work Noda Biyhudah (נודע ביהודה), by which title he is also known. His main work of responsa, titled Noda BiYehudah (נודע ביהודה, "Known in Judah", a reference to Psalms 76:2 and his father's name), is one of the principal sources of Jewish law of his age. Famous decisions include those limiting autopsy to prevent a clear and present danger in known others. This collection was esteemed by rabbis and scholars, both for its logic and for its independence with regard to the rulings of other Acharonim as well as its simultaneous adherence to the writings of the Rishonim.
In 1745 he became rabbi of Yampol. While in Yampol, he attempted to mediate between Yaacov Emden and Yonathan Eybeschütz in a debate—"The Emden-Eybeschütz Controversy"—that "had disrupted Jewish communal life for many years". His role in the controversy is described as "tactful" and brought him to the attention of the community of Prague—where, in 1755, he was appointed rabbi. He also established a Yeshiva there; Avraham Danzig, author of Chayei Adam, is amongst his best-known students.
Rabbi Ezekiel is the author of the following important books:
- Tziyyun Lenefesh Chayah (Memorial to a Living Soul – Shir haShirim 5,10), commentaries on the Talmud. A tribute to his mother named Chayah. This book is often referred to by the abbreviation TZeLaCH.
- Ahavath Zion (Love of Zion)-a book of sermons.
- Derush Lezion (Sermon for Zion). His first published book is 13 sermons he delivered each as the Rabbi of Yampol on Shabbos Shuva and Shabbos haGadol from the years 1745-1753.
- Derush Lehesped (Eulogy on Maria Theresa).
- Dagul Merevavah (Preeminent Above Ten Thousand) - notes on the Shulchan Aruch.
- Mareh Yehezkel (Vision of Ezekiel) notes on the Talmud.
