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1)

(a) Rabah and Rav Yosef establish the Machlokes between the Tana Kama in our Mishnah (who validates the Eruv in the tower whose key is lost) and Rebbi Eliezer (who does not) by a *wooden* tower.
How do they explain the Machlokes? How do they dispense with the original problem from 'Hu be'Makom Echad ve'Eruvo be'Makom Acher'?

(b) How do Rabah and Rav Yosef attempt to connect this Machlokes to the Machlokes in the Mishnah in Zavin, where the Tana Kama renders a large cupboard on which a Zav banged, Tamei, whereas Rebbi Nechemyah and Rebbi Shimon declare it Tahor?

(c) How exactly, did the Zav bang the cupboard, and why must we say that?

(a) Abaye refutes this explanation on the basis of a Beraisa in Zavin. Which fundamental principle did he learn from the Beraisa that clashes with Rabah and Rav Yosef's explanation?

(b) When does a Zav render Tamei what he moves (even if it is an Ohel), and when does he *not* (even if it is a vessel)?

(c) How does Abaye explain the Machlokes between the Tana Kama and Rebbi Nechemyah and Rebbi Shimon?

(a) How do Abaye and Rava (who establish our Mishnah by a wooden tower) explain the Machlokes there between Rebbi Eliezer and the Rabbanan?

(b) Why is there no Isur d'Oraysa per se in cutting the rope?

(c) We are speaking about placing an Eruv on Erev Shabbos during Bein Hashemashos.
Will it also be permitted to cut the rope on Shabbos?

(a) If the Eruv rolls away before Shabbos, under which conditions will it become invalidated?

(b) Is the Eruv still valid if a pile of stones fell on it, or it got burnt, or if it was Terumah and became Tamei?

(c) Why does the pile of stones, which is no more than a question of Muktzah, render the Eruv invalid? Does this mean that the author of *this* Mishnah is *not* Rebbi (although the author of the previous Mishnah's *was*?)

(d) What is the Din if any of the above occur *on* Shabbos?

(a) If one is in doubt whether the Eruv became Tamei before Shabbos or on Shabbos, Rebbi Meir and Rebbi Yehudah say 'Harei Zeh Chamar Gamal'.
What does this mean, and why do they use this term?

(b) What do Rebbi Yossi and Rebbi Shimon hold in this matter?

(c) Why does the Tana need to mention that both an Eruv that rolled away and one on which a pile of stones fell are invalid? Why will either one not suffice?

(d) And why does he need to mention both when the Eruv got burnt and when it became Tamei?

6)

(a) In which case, in the Mishnah in Mikva'os, does Rebbi Meir agree that a Tamei person who is in doubt whether he Toveled or not, remains Tamei?

(b) When does he hold that he is Tahor mi'Safek?

(c) What does Rebbi Yossi hold in this case?

(d) Which two other cases of Safek (i.e. even if he is certain that he Toveled) does the Mishnah include in this Din?

(a) What is difficult (from his own opinion by Safek Taval) with Rebbi Meir's stringent ruling regarding the Safek (whether the Eruv became Tamei before Shabbos or on Shabbos) in our Mishnah?

(b) How do we resolve this?

(c) What size rope is used to measure the Techum Shabbos?

(a) With regard to measuring the distance in order to place an Eruv, Rebbi Meir is quoted as saying 'Im Eino Yachol Lehavli'o ... Shama'ti she'Mekadrin he'Harim'.
What does 'Yachol Lehavli'o' mean?

(b) What does 'Shama'ti she'Mekadrin he'Harim' mean?

(c) How do we measure hilly land with regard to the Techum of an Ir Miklat or the distance between two towns with regard to an Eglah Arufah? Why do we not apply 'Mekadrin he'Harim' there too?

(d) In that case, if Rebbi Meir holds that Eruvin are d'Oraysa, how can he say 'Mekadrin be'Harim' *there*?

(a) The Chachamim, in a Mishnah in Taharos, rule that someone who touched a Safek Chai, Safek Mes during the night, and in the morning he was found to be dead, is Tamei.
Why is that?

(b) What does Rebbi Meir hold, and how does that clash with his opinion in our Mishnah regarding Eruv?

(c) Why does the Gemara reject the suggestion that really Rebbi Meir goes after the Chazakah to be lenient even by a Safek d'Oraysa, but our Mishnah speaks when there was a Sheretz on the Eruv during the entire Bein Hashemashos, in which case, there *is* no Chazakah?

(d) Rabah and Rav Yosef answer this by establishing our Mishnah by two pairs of witnesses (whereas the Mishnah in Taharos speaks when there were none). What does this mean?