Abstract: Planacentric gear box having at least one gear wheel with external teeth (8) meshing with a gear ring with internal teeth (5) whose number of teeth is slightly bigger than the number of teeth of the gear wheel (8), this gear wheel (8) orbiting inside the gear ring (5) by the means of two eccentrics (27)(28) synchronously and simultaneously driven by prime reducers having a common input shaft, planacentric gear box for which the eccentic bearings (23)(24) are located outside the gear ring (5), the gear wheel with external teeth (8) being fixed on a torque arm (14) passing beside the gear ring (5), this torque arm (14) having, diametricaly opposed, two protuberances (19)(20) receiving each the outer ring of the bearings for the eccentrics (27)(28) which are generating the orbitation of the gear wheel (8), the median planes of the gear wheel (8) and of the eccentric bearings (23)(24) being close one to the other.

Abstract: A second-class two-seater seat (1) that can be converted into a first-class single-seater seat, and vice versa. The second-class two-seater seat comprises two seats (2) two seat cushions (3) and two armrests (4). The two-seater (1) comprises elements (5) for translating at least one of the seat cushions (3) and at least one of the two armrests (4), the seat cushions (3) and the armrests (4) remaining mutually aligned. Translations of the seat cushions and the armrests are obtained by the translation element's (5), allowing the seat cushions that are to be translated and the armrests that are to be translated to be brought closer together when the second-class two-seater seat is converted into a first-class single-seater seat, or the seat cushions that are to be translated and the armrests that are to be translated to be moved further apart when the first-class single-seater seat is converted into a second-class two-seater seat.