[Regarding] a sheet that is [susceptible to becoming] tamei with midras [tumah] and one made it into a curtain, it is impervious to midras [tumah], but it is [susceptible to becoming] tamei with corpse-tumah. From when does it become tahor? Beis Shammai say: From when it is broken. Beis Hillel say: From when it is tied. R’ Akiva says: When it is attached.