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 Gemara 43b [line 31]:
1) [line 1] L'HAVRI'ACH MAYIM - to keep out the water
*3*) [line 4] MASNISIN NAMI DEIKA, D'MEHALECHES LO PELIGEI - that is, it can be inferred from the Mishnah that Rabah is correct, and Rebbi Akiva agrees that there is no Shevisah while the boat is moving (not like the reasoning of Rebbi Zeira).
*4*) [line 13] MASNISIN NAMI DEIKA, D'KETANI SEFINA DUMYA D'DIR - that is, Rav Ashi also brought a proof from the wording of the Mishnah that Rabah is correct (and Rebbi Zeira is wrong; Rebbi Akiva agrees that there is no Shevisah as long as the boat is moving).
*5*) [line 16] HILCHESA, MICHLAL D'PELIGI? IN... - Rashi presents two approaches to this Sugya (the second is in parentheses). According to his first explanation, the Gemara is suggesting that perhaps there is no argument at all between Rebbi Akiva and Raban Gamliel when it comes to a boat; both agree that one may walk the length of the boat, when it is moving, and one may not if it is standing, since we do not say "Shavas b'Avir Mechitzos." Rebbi Akiva differed with Raban Gamliel only with regard to his "Chumra," but not with regard to the letter of the law. Gemara concludes that Raban Gamliel indeed argues with Rebbi Akiva and permits walking the length of the boat even if it is stationary. (See also Maharam and Maharsha's interpretation of Rashi.)
Rashi's second explanation is not completely clear; it appears that he is explaining as follows. Gemara originally thought that Rebbi Akiva agrees with Raban Gamliel that one may walk the length of the boat if it is moving (as the Gemara concluded above; he just was "Machmir" for himself). Gemara proves from the Beraisa that this is not so. Rebbi Akiva prohibited walking the length of the boat even if it is moving, not because one is Koneh Shevisah but because of a Gezeirah that the boat may come to a standstill while the person is walking. Since it is only a Gezeirah, and not the letter of the law of Techumim, the Mishnah uses the term "they wanted (= decided) to be Machmir (= make a Gezeirah) for themselves (based on their own logic)." (M. Kornfeld)
6) [line 19] EMESH - in the evening
8) [line 36] SHEV SHEMA'ATA - seven teachings of Amora'im
12) [last line] NAZIR
13) [line 9] L'VEIS DIN HA'GADOL - the Lishkas ha'Gazis, the place where the Sanhedrin, or the Beis Din ha'Gadol, convened (RITVA)
14) [line 12] MIPNEI HA'TORACH - because of the effort needed in order to greet Eliyahu, which would hinder preparations for Shabbos (RITVA)
15) [line 26] SHEFOFERES - a tube
*17*) [line 29] U'MABIT BAH, V'YEDA KAMAH OMKO SHEL GAI - and he looks through it (while standing at the edge of the wadi, with the Shefoferes approximately parallel to the gentle slope of the wadi) and he will know the depth of the wadi. This is accomplished by standing at the edge of the wadi and then pacing backwards while looking through the Shefoferes until the lowest point of the wadi appears in the Shefoferes. Since he knows the Shefoferes measures a known range (2000 Amos in the case of Raban Gamliel), the distance to the bottom of the wadi equals the range of the Shefoferes minus the distance that he paced backwards.
18) [line 31] KOMASO V'TZILO - see Girsa #1. Knowing your own height, measuring the length of your shadow and the length of the shadow of the palm tree makes it possible to figure out the height of the palm tree.
19) [line 34] MASHPI'A V'OLEH, MASHPI'A V'YORED - he slopes the earth that is on either side of the gravestone in such a way that it provides no shade at that time
20) [line 41] B'D'MALU GAVREI - when there were enough people [to form a human Mechitzah from where he was standing *all the way* to the Techum of the city]