Today’s daf is sponsored anonymously in memory of Moshe ben David, Rav Moshe Feinstein, zt"l. After having suggested that according to the rabbis, one could still possibly not conclude from the word "his beard" that the only way for the leper to shave is with a razor, they reject this suggestion on two counts. Rabbi Eliezer derives from the word "his head," mentioned in a verse regarding the shaving of the leper, that a razor needs to be used for the shaving of the leper. What do the rabbis derive from that verse? They derive from it that the commandment to shave all his hair overrides the prohibition to remove (round) the corners of his head.  Why can't that be derived from the word "his beard" which overrides the prohibition to remove the corners of his beard? Why are both necessary? From "the head" we learn both that the prohibition to remove (round) the corners of his head applies even to one who is removing all the hair on one's head and that a positive commandment overrides a negative commandment (shaving of leper overrides removing the corners). From "the beard" we learn that a razor must be used for the leper's shaving. Rabbi Eliezer learns that a positive commandment overrides a negative commandment from the juxtaposition of tzitzit and shaatnez.