Learn משנה דף לח עמוד ב (on bottom of the Amud)
Learn the Gemara until דף לט (two dots)
What is the question גלגל מאי. What does the Gemara want to know?
Learn ר”ן
https://hebrewbooks.org/pdfpager.aspx?req=37953&st=&pgnum=585
& ריטב”א
https://hebrewbooks.org/pdfpager.aspx?req=40905&st=&pgnum=17
Learn חידושי ר”ן for a different explanation in the question of the Gemara.
https://hebrewbooks.org/pdfpager.aspx?req=40873&st=&pgnum=48
https://hebrewbooks.org/pdfpager.aspx?req=40873&st=&pgnum=49
Learn “משנה דף קמה עמוד ב “כל שבא בחמין
What is the proof the Gemara wants to bring from this Mishna?
What melacha of Shabbos is person violating when rinsing old salted fish and Spanish mackerel?
Learn “תוס’ דף לט. “כל