This is from your websites Halachah Outlines: Shulchan Aruch (ibid.): If it is 10 or more, if it is four wide it is Reshus ha'Yachid. If not, it is Mekom Petur, even if there is room in it to carve out and complete four.
What does it mean by if you carve out and complete four? If it's less than four how can you carve out more than it's physical shape?
Thank you,
Eliyahu, NY USA
Thank you for pointing this out, I apologize for leaving this difficult matter unexplained. We will add to the website the Mishnah Berurah's Perush:
Mishnah Berurah (40): I.e. even if the post is next to a wall, and if we would consider the wall and post to be one joint entity, it would contain within it a square four by four, since the post itself does not contain such a square, it is Mekom Patur.
Pesach Feldman
Kollel Iyun Hadaf