1)

(a)The proof from our Mishnah (that when the boat is moving, even Rebbi Yehoshua and Rebbi Akiva permit one to walk the entire boat - like Rabah) - is from the Lashon 'she'Ratzu Lehachmir al Atzman', from which we can infer that, strictly speaking, they were permitted to carry on the entire boat - because it was moving (like the contention of Rabah), and that they only declined to do so because they wished to be Machmir on themselves, because maybe, the boat had stopped moving for a short while, in which case, they would have been Koneh Shevisah, and would indeed be forbidden to walk more than four Amos.

(b)The Gemara's second proof from the Mishnah, is from the juxtaposition of the Machlokes of the boat, to the case of the man who was forcibly removed by gentiles and placed in an enclosure etc.; just as there, the enclosure is stationary, so too, does the dispute by the boat speak when the boat is stationary.

2)

(a)The Gemara was surprised at Rav Acha Brei de'Rava ruling like Raban Gamliel in the case of the boat - since even Rebbi Yehoshua and Rebbi Akiva only wanted to be strict with themselves, implying that, strictly speaking, they agreed with Raban Gamliel. In that case, why would it be necessary to rule like Raban Gamliel, since nobody argued with him?

(b)The questioner's mistake lay in failure to realize that Rebbi Yehoshua and Rebbi Akiva only agreed with Raban Gamliel by a boat that was moving (as we explained a little earlier), but not when the boat was stationary; and it was there that Rav Acha B'rei de'Rava found it necessary to issue a ruling like Raban Gamliel.

3)

(a)The She'eilah whether Techumin applies above ten Tefachim applies - either to a long but narrow board which is higher than ten Tefachim, but less than four Tefachim wide - (whether one may travel beyond the Techum along that board); or whether someone who is able to fly, due to having pronounced one of the Names of Hash-m (even though doing so is forbidden) - is permitted to do so beyond the limits of the Techum on that Shabbos or Yom-Tov.

(b)If there was no Techum on water above ten Tefachim - then why did Rebbi Yehoshua and Rebbi Akiva want to be strict with themselves. There were absolutely no grounds to be strict here, since, even if the boat did stop (which was the cause of their Chumra), they would still be above ten Tefachim and would therefore be permitted to walk in any case.

(c)There in fact, no proof from there that Techumin above ten Tefachim does apply - because the Mishnah could well be speaking when the boat in question was traveling below ten Tefachim. But had it been higher, then even Rebbi Yehoshua and Rebbi Akiva would have no reason to be strict with themselves.

(d)Nor is there is any proof from those seven Chidushim, which were said one Shabbos morning in front of Rav Chisda in Sura, and again in the afternoon in Pumbedisa in front of Rabah (which was well outside the Techum Shabbos of Sura) - because who said it was Eliyahu ha'Navi who whisked the Chidushim from Sura to Pumbedisa on that Shabbos, perhaps it was Yosef the (learned) Demon?

4)

(a)Why is the 'Nazir' (who has undertaken to be a Nazir on the day that Mashi'ach comes), permitted to drink wine on Shabbos and Yom-Tov? Why do we not suspect that he may still come that very day, in which case the Nezirus will become effective? Unless the Din of Techum applies even above ten Tefachim, in which case we know for sure that Eliyahu cannot have arrived on Friday.

(b)If the 'Nazir' was permitted to drink wine on Shabbos and Yom-Tov because Eliyahu has not arrived by Friday, then he should be permitted to drink wine every day, since, by the same token, Eliyahu had not been known to arrive on the previous day, Mashi'ach would most certainly not come on that day.

(c)Since Eliyahu had not arrived on the previous day, then why was the Nazir not permitted to drink wine on the following day? - is not a Kashya - because it is possible that really, Eliyahu had indeed arrived, but his presence remained as yet, unknown, because he went first to the Beis-Din ha'Gadol to 'present his credentials' as it were.

(d)The reason that the 'Nazir' is permitted to drink wine on Shabbos and Yom-Tov - is on account of the tradition that Mashi'ach will not come on Shabbos or Yom-Tov, not for any intrinsic reason, but because Eliyahu ha'Navi, who will always come one prior to the arrival of Mashi'ach, will not come on Shabbos, in order to interfere with the preparations for Shabbos, which have priority. In other words, people would take the trouble to go and greet him, and that is wrong, because the preparations for Shabbos take precedence.

5)

(a)Eliyahu cannot come on Friday, in order not to interfere with the preparations for Shabbos, as we explained above - but Mashi'ach can. Why? Because the moment Mashi'ach arrives, all the nations will become subservient to us, and we will not be short of servants to prepare Shabbos for us.

(b)There is no proof that there is Techumin above ten Tefachim, because otherwise, why may the 'Nazir' not drink wine on Sunday, seeing as Eliyahu cannot have arrived on Shabbos - because it may well be that the Tana who was really not sure whether Techumin applies above ten Tefachim, forbade the 'Nazir' to drink wine even on Sundays, because maybe there is no Techumin above ten Tefachim, and Eliyahu ha'Navi will arrive on Shabbos (although it is possible that there is, in which case, Eliyahu will not come on Shabbos).

6)

(a)We finally explain the words 'Mutar Lishtos Yayin be'Shabbasos u've'Yamim-Tovim to mean - that if he declared his vow on a Shabbos or a Yom-Tov, he is able to drink wine on that Shabbos or Yom-Tov only.

(b)We are forced to say that - because those are the only day that he could possibly be permitted to drink wine. On any subsequent Shabbos, there is no way that he would be permitted to do so, since he had already become forbidden during the week (and how can the ban to drink wine be lifted?), so the only day that drinking wine can possibly be permitted, is on the first day when his vow was made on a Shabbos, because a. Eliyahu had not come on the previous day - Friday, and b. he had not yet become forbidden to drink wine on the previous day, as would be the case on all subsequent Shabbasos (see Rabeinu Chananel - Rashi's explanation does not appear to follow the text in our Gemara).

7)

(a)Raban Gamliel in our Mishnah knew exactly where the Techum Shabbos ended - by means of a tube whose length he adjusted so that, when he peered down it, his line of vision, via the lower outer edge of the tube would end at exactly two thousand Amos.

(b)In order to ascertain ...

1. ... the height of a date-palm, one would measure one's own height and the length of one's shadow - from which one would know the ratio of his real height to that of his shadow; then he should measure the shadow of the date-palm and apply the same ratio to the palm-tree (twice the height or three times, or whatever it was).

2. ... the depth of a (very shallow) valley - one takes a tube (whose maximum vision limit is for example, two thousand Amos, and moves to the top of the ledge overlooking the valley. Then he moves back, still looking through the tube, until he reaches a point where the valley is no longer visible (due to the fact that it is outside the line of vision of the tube, and not because of the angle of the valley). By detracting the distance from the ledge to where he is now standing, he will know the height of the valley.

8)

(a)To prevent wild animals from resting in the shade of an earthen-tombstone - he should first stick a post in the ground, in order to gauge the direction of the shadow during the hottest time of day (since that is also the direction that the shadow of the grave will stretch). Then, he builds a sloping mound of earth leading off the tombstone in that direction. In this way, the animal will be prevented from taking shelter in the shade of the tombstone at that time of day.

(b)He would stick the post into the ground specifically after four hours - when the sun begins to get hot (which is also the time when wild animals usually come and look for shade).

(c)We are afraid that the animal will not just rest beside the Matzevah, but brush against it and knock it down.

9)

(a)When Rav Nechemyah, Rav Nachman's disciple, engrossed in his studies one Shabbos, walked straight outside of the Techum - Rav Nachman instructed them to make a human Mechitzah to enable him to return.

(b)No! Rav Chisda had no problem with the She'eilah of whether a Mechitzah that is made on Shabbos would be effective to permit Rav Nechemyah to return to inside the Techum) - since Rav had already ruled like Raban Gamliel, with regard to both gentiles who removed someone from his Techum forcibly (to which our case - where Rav Nechemyah left his Techum be'Ones, is comparable) and walking the entire ship which traveled beyond the Techum on Shabbos. What he wanted to know was whether the Halachah was like Rebbi Eliezer, who permits someone who has walked two Amos outside his Techum (and no more) to return to his Techum, under any circumstances. In our case, the She'eilah therefore was whether - if there were enough people to form a Mechitzah up to within two Amos of Rav Nechemiah's original Techum, he would be permitted to return the final two Amos into his Techum, even without an Eruv - like Rebbi Eliezer.

(c)We know that this is so from Rav Nachman, who replied 'Make him a Mechitzah of people, and let him enter'. Now it is obvious that once they made him a Mechitzah of people, he would be allowed to enter (otherwise why would they have taken the trouble to make the Mechitzah?) What he must therefore have meant is, that they should make Rav Nechemyah a Mechitzah of people, and, in spite of the fact that the Mechitzah ended two Amos short of his Techum, he was nevertheless permitted to enter - like Rebbi Eliezer.