1. One may not make a doorway opposite his neighbor's doorway.
2. The Gemara cites a source for this law from Bil'am's inability to curse Bnei Yisrael.
3. One is allowed to make a doorway opposite another doorway that is on the other side of a public domain.
4. Rebbi Yanai and another person had trees whose branches were hanging over the public domain.
5. Rebbi Yanai told the other person to come back for his judgment the following day.
A BIT MORE
1. Similarly, he should not make a window opposite his neighbor's window.
2. The verse relates that Bil'am could not curse Bnei Yisrael after he saw them "dwelling according to its tribes." The Gemara infers that he must have seen that the entranceways to their tents did not face each other. He realized that, with such a degree of modesty, it was appropriate for the Shechinah to rest upon Bnei Yisrael.
3. This is because the homeowner may say that he is not different from any of the other people in the public domain.
4. People complained to Rebbi Yanai that the second person's overhanging branches disturbed them.
5. Rebbi Yanai first wanted to cut down his own tree, which he originally had thought would benefit the people by giving them shade, and only then could he order the other person to cut down his tree as well.