A set includes two blocks each of two seats convertible for lying down, wherein the two blocks are arranged with the seats of one block face-to-face with the seats of the other block inside a circumscribed rectangle. Each block includes a first seat and a second seat. The first-seats of the two blocks are arranged along a first diagonal of the circumscribed rectangle and the longitudinal axes of the first seats are oriented so that their directions are close to the first diagonal and the first seats are substantially face-to-face. The distance between the two first seats is such that a foot area of a first seat of a block is superposed when seen from above with a foot area of the first seat of the other block. In the recumbent configuration, the planes to lie down on of the two first seats are at different heights.