PBA: Yes, Rav Schachter proves from the Mishnayos about a Sukkah in an Aliyah that as a prerequisite for having a Sukkah you need 4 walls and a floor. (It was in his Shiur online on Inyanei Sukkah from last week, if you want to go back and listen to it.)
Shein: Fine, I apologize for faking humility on Motza’ei Yom Kippur and not using a more definitive statement and said “probably”. I’m sure of it. When I’m not sure I say so. I think I’ve been posting here long enough for you to realize that. When I say “probably” it means I’m sure I’m right. I’m sorry for using a Lashon that confused you.