MB4 196a: The Four Domains of Shabbos (345:1-3)
The four domains of Shabbos: public, private, karmelit, and makom petur.
The definition of a reshut hayachid (private domain): an area enclosed by four walls that is at least 4 tefachim square. How do we calculate the four tefachim?
The status of the walls enclosing a reshut hayachid