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1)

(a) How does the Gemara initially reconcile Rebbi Yossi in our Mishnah (where he places the Eruv on a Chezkas Taharah), with his own opinion in the Mishnah in Mikva'os (of Safek Taval, where he declares him Tamei - even by a Tum'ah de'Rabbanan)?

(b) An alternative answer is that the opinion that he cites in our Mishnah is not his own, but his Rebbe's.
Who is his Rebbi and what did he say in the name of five elders?

(c) Rava explains that Rebbi Yossi is strict by Safek Taval, because the person has a Chezkas Tum'ah.
Why do we not contend with the Chezkas Taharah of the Mikvah?

3)

(a) The Beraisa differentiates in Rebbi Yossi between whether 'Safek mi'be'Od Yom Nitma'as, Safek mi'she'Chasheichah Nitma'as', and 'Erav bi'Terumah, Safek Tehorah Safek Temei'ah'.
What is the difference between them?

(b) The Beraisa incorporates in the former case: 've'Chen Peyros Safek mi'be'Od Yom Niskanu, Safek mi'she'Chasheichah Niskanu'.
Why can this not be referring to Safek Tevel?

(c) What then, is it referring to?

(a) If someone designates for his Eruv, whichever of the two Terumah loaves lying in front of him which is Tahor, why might ...

1. ... Rebbi Meir concede that his Eruv is valid?
2. ... Rebbi Yossi concede that it is not?

(b) The Gemara concludes that the Eruv is invalid according to both Tana'im.
Why is that?

(c) Why can a loaf which the owner declared Chulin on Friday and Hekdesh on Shabbos, make a valid Eruv, whereas if he declared it Hekdesh on Friday and Chulin (redeemed) on Shabbos, it cannot - even though both have the same Safek during the Bein Hashemashos period?

(d) What did Rav Nachman mean when he said to Rava 'Lechi Teichol Aleih Kura de'Milcha'?

(a) The Mishnah in Tevul-Yom rules that if, on Friday, a Tevul Yom declares Terumas Ma'aser when Shabbos enters, a jar of wine which he drew from a barrel of Ma'aser Rishon wine from which Terumas Ma'aser had not yet been separated - his declaration is effective.
Why will this jar of wine not then be eligible for an Eruv? What does Rava prove from here?

(b) How does Rav Papa refute Rava's proof?

6)

(a) Our Mishnah writes 'Masneh Adam al Eruvo ve'Omer "Im Ba'u Nochrim min ha'Mizrach (or 'min ha'Ma'arav'), Eruvo Eruv"'. Which basic principle does this Mishnah come to teach us?

(b) Which other case (other than that of 'Ba'u Nochrim') does the Tana insert?

(c) In which case does Rebbi Yehudah disagree with the Tana Kama, and what does he hold?

(d) Why does the Tana Kama argue with Rebbi Yehudah?

8)

(a) Rav disregards our Mishnah in view of the opinion of Ayo, who quotes Rebbi Yehudah as saying that an Eruv that is made in two opposite directions, on the condition that in whichever direction the Chacham arrives, his Eruv should be valid, is not in fact, valid.
Why not?

(b) Then why is it not considered 'Bereirah' even if the Eruv is only placed in *one* direction, on the condition that the Chacham arrives there?

(c) Rav preferred to disregard our Mishnah in face of Ayo, rather than vice-versa. This is on account of the Beraisa of 'ha'Lokei'ach Yayin mi'Bein ha'Kutim' etc. What does Rebbi Yehudah say there, and how did that influence Rav?