Siman - Berachos Daf 49

• Don't conclude berachah with two subjects

The Gemara explains that we don’t conclude a berachah with two subjects because we don’t perform mitzvos in bundles – אין עושין מצות חבילות חבילות.

-For example, we don’t conclude the berachah of Birkas Hamazon with בונה ירושלים (Builder of Yerushalayim) andמושיע ישראל  (Savior of Israel).

• Forgot to say יעלה ויבא

Rav Nachman explains logically why when one forgets to say יעלה ויבא in his Rosh Chodesh tefillah he must repeat it, but when he forgets to say it in Rosh Chodesh bentching, he doesn’t repeat it:

-Tefillah is obligatory, so it must be repeated with the proper mentioning of Rosh Chodesh.

-Eating bread on Rosh Chodesh is not obligatory, so there is no need to repeat bentching if יעלה ויבא was forgotten.

• Minimum amount of bread to be obligated in a zimun

The Gemara explains the machlokes between R’ Meir and R’ Yehudah regarding the minimum amount of bread one must eat to be obligated in joining a zimun.

-R’ Meir says it’s a כזית, because he interprets ואכלת as referring to אכילה and ושבעת as referring to שתיה, and the minimum shiur for אכילה is a כזית.

-R’ Yehudah says it’s a כביצה, because he interprets the words ואכלת ושבעת together as referring to אכילה שיש בה שביעה (the eating of an amount that satiates), which is a כביצה.