MB4 249a: Retracting a Nullification by Inheritors or Retracting Multiple Times (381:4-7)

Being mevatel your house but leaving a room behind (שלא תשכח תורת עירובין).

Two houses on either side of a reshut harabim and a gentile comes and encloses the area with a fence on Shabbos, making the area into a chatzer. Can it be used?

If someone inherits a property on Shabbos can he be mevatel his reshut?

Can you retract your nullification on Shabbos and then nullify your reshut again?