What is the reason that you did that? Why did you kill only the males? Joab said to him: As it is written: You shall blot out the males [zakhar] of Amalek, i.e., the male descendants of Amalek, who descend from Edom. David said to him: But we read the verse as stating: “You shall blot out the remembrance [zekher] of Amalek” (Deuteronomy 25:19). Joab said to him: I was taught to read it as zakhar. Joab went and asked his childhood Bible teacher. Joab said to him: How did you read this word to us? The teacher said to him: I read it as zekher. The teacher had read it the proper way, but he failed to notice that his student had learned it incorrectly.

Joab took a sword to kill him. The teacher said to him: Why do you want to kill me? Joab said to him: As it is written: “Cursed is he who does the work of the Lord with a slack hand” (Jeremiah 48:10), and you taught me incorrectly. The teacher said to him: Leave that man to remain as cursed. This is a sufficient punishment; there is no need to kill me. Joab said to him: It is also written: “And cursed is he who keeps back his sword from blood” (Jeremiah 48:10). There are those who say that Joab killed him, and there are those who say that he did not kill him. In any event, this episode demonstrates that an error learned in one’s childhood stays with him his whole life.

And Rava says: With regard to a teacher of children, a professional tree planter, a butcher, a bloodletter, and a town scribe, all these are considered forewarned. In other words, they need not be exhorted to perform their jobs correctly, as if they err in the performance of their duties they can be dismissed immediately. The principle of the matter is: With regard to any case where loss is irreversible, the individual is considered forewarned.

§ Rav Huna said: There was a certain resident of an alleyway who set up a mill in the alleyway and earned his living grinding grain for people. And subsequently another resident of the alleyway came and set up a mill next to his. The halakha is that the first one may prevent him from doing so if he wishes, as he can say to him: You are disrupting my livelihood by taking my customers.

The Gemara suggests: Let us say that a baraita supports his opinion: One must distance fish traps from fish, i.e., from other fish traps, as far as the fish travels, i.e., the distance from which the fish will travel. The Gemara asks: And how much is this distance? Rabba bar Rav Huna says: Up to a parasang [parsa]. This indicates that one must distance himself from the place where another has established his business. The Gemara responds that this is no proof: Perhaps fish are different, as they look around. One fish explores the area ahead of the others, indicating to them where to go. Once they encounter the first trap they will not approach the second.

Ravina said to Rava: Shall we say that Rav Huna spoke in accordance with the opinion of Rabbi Yehuda? As we learned in a mishna (Bava Metzia 60a): Rabbi Yehuda says: A storekeeper may not hand out toasted grain and nuts to children who patronize his store, due to the fact that he thereby accustoms them to come to him at the expense of competing storekeepers. And the Rabbis permit doing so. This indicates that according to the opinion of Rabbi Yehuda, all forms of competition are prohibited, which would include the scenario concerning the mill.

The Gemara rejects this suggestion: You may even say that Rav Huna holds in accordance with the opinion of the Rabbis. The Rabbis disagree with Rabbi Yehuda only there, as the storekeeper can say to his competitor: If I distribute walnuts, you can distribute almonds [shiyuskei]. But here, with regard to a resident of an alleyway who sets up a mill in that alleyway where another mill already exists, even the Rabbis concede that the owner of the first mill can say to him: You are disrupting my livelihood, as beforehand whoever required grinding came to me, and you have provided them with another option.

The Gemara raises an objection from a baraita: A man may establish a shop alongside the shop of another, and a bathhouse alongside the bathhouse of another, and the other cannot protest, because the newcomer can say to him: You operate in your space, and I operate in my space.

The Gemara answers: This entire matter is a dispute between tanna’im, as it is taught in a baraita: The residents of an alleyway can compel one another to agree not to allow among them in that alleyway a tailor, a tanner, a teacher of children, nor any type of craftsman. They can bar outside craftsmen from plying their trade in that alleyway. But one cannot compel his neighbor, i.e., one who already lives in the alleyway, to refrain from practicing a particular occupation there. Rabban Shimon ben Gamliel says: One can even compel his neighbor not to conduct such work in the alleyway. Rav Huna holds in accordance with the opinion of Rabban Shimon ben Gamliel.

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 from doing business there, as he too is considered a resident of the town. The resident of an alleyway cannot prevent a resident of his alleyway from practicing a particular trade there, in accordance with the opinion of the Rabbis in the baraita, and contrary to the opinion of Rabban Shimon ben Gamliel.

With these conclusions in mind, Rav Huna, son of Rav Yehoshua, raises a dilemma: With regard to a resident of one alleyway protesting about a resident of another alleyway conducting business there, what is the halakha? No answer was found, and the Gemara states that the dilemma shall stand unresolved. Rav Yosef said: And 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 him from working, as the Master said: Ezra instituted an ordinance for the Jewish people requiring that they establish one teacher alongside another teacher, to raise the standard of teaching.

The Gemara challenges: And let us be concerned lest the teachers will thereby come to be negligent. Rav Yosef said to the Sage who raised this objection: