Learn the גמרא דף לז. “איבעיא להו until “ת”ש (fifth wide line)
Question:
Is the question whether סמיכה is permitted in to שהייה or חזרה?
Learn תוס’ “מהו
If the question of the Gemara is in regards to חזרה what is the proof from the braissa which only discusses שהייה?
Learn רי”ף which brings a proof from this question the halacha is like רבנן
https://hebrewbooks.org/pdfpager.aspx?req=37953&st=&pgnum=581
Learn רשב”א for a different explanation of the question of the Gemara
https://hebrewbooks.org/pdfpager.aspx?req=40907&st=&pgnum=56