Study Guide Eruvin 95 Do Rava and Abaye disagree about whether or not we can use imaginary walls created by a ceiling, pi tikra yored v'sotem (when there are no actual walls on any side), as Rav and Shmuel disagree? Does Rabbi Yosi in the mishna who disagrees with Rabbi Yehuda (that the beginning of Shabbat is the determining factor) permit in these cases or forbid? Do we hold like Rabbi Yehuda or Rabbi Yosi? Shmuel holds like Rabbi Yehuda, however the gemara questions that based on a different source. The mishna discusses cases of a bridge or a second floor built over the public domain - can one carry beneath it? On what basis would it be permitted? Can one fix (make an eruv) an alley that is open on two sides? On what basis could one permit? The tenth chapter begins with a discussion of tefillin found in a field. One is obligated to "save" them. How can one carry them on Shabbat - only if they wear them? Tana Kama and Rabban Gamliel disagree about whether one wears one pair or two at a time . What is the root of their debate? Does it connect with other basic debates such as, is one supposed to wear tefillin on Shabbat, do mitzvot need intent in order to fulfill them, is it forbidden due to bal tosif, adding to mitzvot, to wear two pairs at a time?