Likutei Sichos vol. 19 page 55 ff. The authority of neighborliness in Torah, Class One.

Likutei Sichos vol. 19 page 55 ff. The authority of neighborliness in Torah, Class One.
This incredibly precise and scholarly Sicha is (officially a Siyum on Meseches Suka, but it is so much more) discusses the authority the Rabbis have in developing the vague and all inclusive Divine commandment of ועשית הישר והטוב (that Jews should be civil and decent and generous to one another).
One of the areas that this law affects is neighbors, and our Sicha explores what turns out to be a dispute between RaShI and the RaMbaM (!!!). RaShI limits the authority of Halacha regarding neighborliness, while the RaMbaM gives incredible authority to the ChaZaL in this area.
The Rebbe uses three examples for this (two of which are in this class, and we left the third for our second class on this Sicha).
A. בר מיצרא physical land-owners who are neighbors, to what extent are the bound to each other by this Mitzvah and Halacha.
B. תוספת שבת when one adds more time to Shabbos (or Yom Tov) before and after, can he make Kiddush during this extra time (as the neighbor of Shabbos)? This is determined by the nature of this neighborliness.