Study Guide Shabbat 157 The Siyum is sponsored in memory of Rabbi Adin Even Yisrael Steinsaltz zt”l a true giant in Torah learning and a leading educator of our generation who made talmud accessible to all. And by Roslyn Jaffe in honor of the seventh Yahrzeit of her wonderful father Mickey Muhlrad, A”H, Moshe Yaakov Ben Dovid. He followed in Hashem’s ways with his kindness, chesed and love for Yiddishkeit and learning. He had great respect for talmidei chachamim and would be so proud of all the women learning Daf Yomi. And for a refuah shleima to Elchanan David ben Yatza Ruth and Tzippora bat Charna.  Can one nullify or dissolve vows on Shabbat? What is the difference between nullifying and dissolving? Does it matter if it is for the purposes of Shabbat or not? What if one could have done it before Shabbat and didn't? The rabbis take a situation that happened relating to a case of potential impurity from a dead body and derive from there that certain things are permitted for the purposes of a mitzva. The gemara ends with a story of a rabbi measuring a tub of water and when approaced by Ulla and questioned how one can do this, he responded that he was not measuring for any purpose - mitasek - and therefore it was permitted.