Halachah and Tosfos in the Days of the Omer

Rav Menachem Mendel said that he had never understood the secret of the matter until recently: the laws and halachos that were forgotten during the mourning over Moshe Rabbeinu (see Temura 16a) were returned to us by Osniel ben Kenaz during the days of Sefiras HaOmer. Therefore it is a minhag Yisroel, which has the status of Torah, to study halachah and Tosfos during these days.