Hasagat G'vul: The limits of Rabbi'ing in the Online World (Are there any?)

(14) You shall not move your countryman’s landmarks, set up by previous generations, in the property that will be allotted to you in the land that the LORD your God is giving you to possess.

. . . One who does not allow the poor to gather gleanings, or one who allows one but not another, or one who helps one of them [to gather] behold he is a robber of the poor. Concerning him it is said: “Do not remove the landmark of those that come up.” (Proverbs 22:28).

Rav Huna said: A certain resident of an alleyway who set up a mill, and then another resident of the alleyway came and set up a mill next to his. The law is that he [the first one] may prevent him , as he can say to him: You are disrupting my livelihood.

Let us say that the following teaching offers support for his opinion: One must distance fish traps from fish, [i.e., from other fish traps] as far as the fish travels. Which is how much?

Rabba bar Rav Huna says: Up to a parasang [parsa].

[But, that is not a good support since] fish are different, as they look around.

Rav Huna, son of Rav Yehoshua, says: It is obvious to me that a resident of one town can prevent a resident of another town [from establishing a similar business in the locale of the first individual]. But if he pays the tax of that first town, he cannot prevent him. The resident of an alleyway cannot prevent a resident of the same alleyway.

Rav Yosef said: And [even] Rav Huna [who said that a resident of an alleyway can prevent another from setting up an additional mill] concedes with regard to those who teach children that one cannot prevent another from working, as the Master said: Ezra instituted an ordinance for the Jewish people allowing that they establish one teacher alongside another teacher . . .

Jealousy among teachers increases wisdom.