Computation of the Probability of the Best Derivation of an Initial Substring from a Stochastic Context-Free Grammar

A webbing guide apparatus is arranged such that an intermediate portion of a shoulder webbing is guided by a guide means provided on a head rest for the purpose of allowing an occupant who is to seat himself or is seated in the back seat of a two-door vehicle to smoothly enter or leave the vehicle. When the seat back rest is inclined toward the front of the vehicle, the angle of pivoting of the guide means with respect to the head rest is properly limited such that the intermediate portion of the webbing is moved upwardly forward of the vehicle in response to the forwardly inclining movement of the seat back rest, thereby enlarging the space where the occupant of the back seat of the vehicle moves when entering or leaving the vehicle.