Today's daf is sponsored by Leslie Glassberg Nadel in memory of her mother, Tova Bat Zvi Hirsch z"l and by an anonymous donor in loving memory of Emuna Bracha Esther and in honor of the incredible women in her life (both mentors and students) who are learning daf yomi.  The gemara brings four explanations regearding the debate between Rabbi Yehuda and Tana Kama about one who takes out a promissory note on Shabbat - if it is after it was paid back, is one obligated? Is it still a useful item? What is the basis for the debate and what exactly are the circumstances? Rava asks Rav Nachman about the requisite amount for taking out the hide of an animal at different stages - before it was processed, once it was processed, etc. Rav Nachman says it is the same for all. The gemara raises several questions on this from other cases where we distinguish between an item before it is processed and after. The mishna gave a size for parchment for tefillin. But in a braita a different amount appears in the context of tefillin and mezuza. The gemara distinguishes between tefillin and mezuza. However it is difficult as tefillin is generally made of klaf and mezuza on duchsustos and the braita mentioned both in relation to tefillin. The gemara rereads the braita to line up each type of parchment with what it can be used for. Rav says that one can use duchtostos for tefillin. The gemara raises several questions on this and also tries to bring a potential proof but ultimately concludes that Rav's statement was the reverse -that one can use klaf for mezuza.