List the two different explanations (Rashi & Tosfos) of the chidush of Rav Sheshes and Rav Oshia דף לח עמוד ב that Beis Hillel permits חזרה even on Shabbos.
Learn the ר”ן דף יז: דפי הריף ” ומיהו בירושלמי which brings a new explanation for the chidush of Rav Sheshes
https://hebrewbooks.org/pdfpager.aspx?req=37953&st=&pgnum=584
Why does Beis Shammai prohibit Chazara even on a stove that is גרוף וקטום ?
See רש”י דף לו: “לא מחזירין
Is this the same reason Beis Hillel prohibits if it is not גרוף וקטום ?
According to Chanania it is permitted to leave food that is half way cooked on a stove that is not גרוף וקטום. Yet in regards to chazarah Beis Hillel only permits Chazara on a stove that is גרוף וקטום. Why?
Learn ח’ ר”ן דף לו: “אין מחזירין
https://hebrewbooks.org/pdfpager.aspx?req=37953&st=&pgnum=580
Continue learning the גמרא דף לח: “א”ר זריקא (seven lines from the top of the Amud) until the Mishna