פירוש על עירובין 9:3

"Not! For [according to] the whole universe that is allowed. Rather, this is that about which they argued: One master reasoned 'beam" -- As the Sages had decreed in the case of an alleyway on the basis that it is an obvious delineation of private space, QED! Thus is a delineation in entrances analogous to "utilization beneath the beam."