Very quickly review the גמרא דף ט.”א’ל רב הונא בריה דרבי יהושע (twelve lines from bottom of the Amud) until דף ט: “ולרבי שמעון בן גמליאל (sixth line from top of the Amud)
Is the reason for אביי connected to his opinion that Lechi is a mechitza?
Learn the ריף
Note: the requirements that the Rif specifies to allow one to carry between the Lechi.
Learn the בעל המאור who disagrees with the Rif
Learn the מלחמת ה who defends the conclusion of the Rif
https://hebrewbooks.org/pdfpager.aspx?req=14312&st=&pgnum=329
In conclusion what is the reason
That אביי says בין לחיים אסור
That רבא says it’s מותר