I know that most people are unclear about the issue of three trees. Or at least that is what I imagine to myself. After all I do not see anyone walking around at the sea that is worrying about that confusing issue in Bava Batra page 26. Or maybe they all have it clear so it does no bother them anymore. But at least for me I should say that in spite of my having written a few ideas on the Tosphot, still I am unclear. One thing that has helped is looking at Rav Shach's Avi Ezri on Laws First Fruits.
Just as an introduction let me just bring some basic facts. Ula said one who has owns a tree within 16 amot [circa yards] of the boundary of his friend, can not bring first fruits since he is a thief. [Thank God that someone noticed the problem. Rav Shach brings the Rashba on page 81 that asks this very question. There it says: one who buys tree owns around it כמלא אורה וסלו around it the width of one that plows and his basket. The Rashba asks the obvious question: That is not 16 amot!
Rav Shach himself brings this long and difficult subject and brings a few answers.
That does not look like the Mishna where there is an argument about how close to the boundary of his friend one can dig a pit or plant a tree. R.Yose says he can go right up until the edge, since one plants in hi own, and the other digs in his own.
