Study Guide Rosh Hashanah 18 Today's Daf is sponsored by Rina Goldberg in memory of her aunt, Valley Densa, z"l, "who lived to the age of 100 plus. She, like her siblings, was educated in the Hildesheimer Yeshiva in Berlin and lived a life replete with Chesed." And by the Fortinskys "Mazal tov to Goody and Eric Weil, on Netanel and Adina's wedding."  Is repentance strong enough to repeal a divine decree that has been sealed, even for an individual? There is a tannaitic debate on this issue. Can one definitely repeal a divine decree for the community? There are verses that seem to suggest otherwise. How can this be understood? When they would sanctify the new moon and determine the first day of the month, they would send messengers to let people know of the date of the new moon so that they would know when to celebrate holidays and fast days. Since not all the months have holidays and fast days, they would only send out messengers six months of the year. Why not for Tevet and Tamuz that also have fast days? The nature of those fasts is different as derived from a verse in Zecharia as the nature of the day and the nature of the obligation changes in a time of peace, when the enemy rules, and when it is neither. There is a debate between Rabbi Akiva and Rabbi Shimon regarding the dates of some of the fasts and what is the event for which we are fasting. Megillat Taanit was a book listing days on which miracles happened so that people would know that it is forbidden to fast and eulogize on those days. Was that book cancelled after the Temple was destroyed, just as the fast were reinstituted or not? It is a subject of debate. The Gemara raises questions against those who say that it was cancelled.