Today's daf is dedicated to Ariella Radwin. Happy Birthday Ariella, the Talmud scholar of the Radwin family! We are so proud of your commitment to study the daf yomi and to share your love of Torah and learning in our house. A student cannot teach a halacha in front of his rabbi. Can he check a shechita knife for himself without asking his rabbi? Can he teach a halacha if his rabbi is not there? Or if he is not in the rabbi's hometown? Or if he is a colleague? Can one reprimand someone doing something wrong if his rabbi is there? Nadav and Avihu were killed for teaching a halacha in front of Moshe. One cannot give all of one's gifts to the priests to one particular priest - it will cause famine in the world (proof from King David). Elazar the priest was also punished for teaching in front of Moshe. Why was Yehoshua punished that he did not have sons - was it also for this reason or because he prevented the nation from being able to reproduce by keeping them in battle at night thus preventing the men from coming home to their wives. The gemara gets back to the topic of eruv chatzerot and brings a story where there was a non-Jew named Lachman bar Ristak who was living in a courtyard with Jews and would not rent out his property to them. What was suggested that they do and was this a valid suggestion?