Study Guide Pesachim 71 Ulah said in the name of Rabbi Eliezer that whole people who slaughtered a chagiga on the fourteenth day and ate it on the fifteenth day, do not fulfill their obligation for peace offerings of simcha or for peace offerings of chagiga that were brought on the holiday. Why? A braita is brought to support and a braita and mishna are brought to contradict but all are rejected/resolved. Ravin brings a different version in the name of Rabbi Elazar – that it can be used for peace offerings of simcha. The gemara questions this from a bratia and resolves the difficulty. Rabbi Kahana provides proof that the parts of the chagiga that get burned of the altar are disqualified by the morning if not burned overnight.  Rav Yosef questions his proof. Abaye counters Rav Yosef’s question and as a result Rava reinterprets the question. If one makes a mistake while trying to perform a mitzvah and for example sacrifices an animal for a Pesach sacrifice on the fourteenth on Shabbat but does it in a way that disqualifies the sacrifice. Retroactively, he has now desecrated Shabbat. What is used for determining under what circumstances one will be obligated to bring a sin offering? Rabbi Eliezer and Rabbi Yehoshua disagree regarding some cases. The mishna brings a discussion between Rabbi Eliezer and Rabbi Yehoshua trying to prove their position and disprove the other. Rabbi Meir adds a more lenient approach to this matter.