Learn משנה דף יא: “הכשר מבוי
Question:
Why does Beis Shammai require a Lechi plus a Korah?
Learn the Gemara from the Mishna until the two dots.
Questions:
What is the inference from the mishna that implies Beis Shammai requires four walls to create a Reshus Hayachid?
Learn “ריטב”א דף יא: “לימא קסברי
Learn beginning of “רשב”א דף יא: “לימא קסברי
The Gemara seemingly concludes that according to Beis Shammai three walls are required to create a Reshus Hayachid.
And according to Beis Hillel only two walls are needed.
Is this indeed the Halacha that only two walls are needed to create a Reshus Hayachid?
Learn ריטב”א דף יא: “הדר אמרינן
Learn the rest of רשב”א דף יא: “לימא קסברי to explain the conclusion of the Gemara.
Note the גירסא change of the הגהות הגר”א (side of the Gemara)
What changes in conclusion of the gemara according to the גירסא change of the גר”א
Learn רמב”ם ה’ שבת פרק י”ד הלכה א
https://hebrewbooks.org/pdfpager.aspx?req=14278&st=&pgnum=57
https://hebrewbooks.org/pdfpager.aspx?req=14278&st=&pgnum=58
and פרק י”ז הלכה ט
https://hebrewbooks.org/pdfpager.aspx?req=14278&st=&pgnum=73