The parallel parking problem is a motion planning problem in control theory and mechanics to determine the path a car must take to parallel park into a parking space.
The front wheels of a car are permitted to turn, but the rear wheels must stay aligned.
When a car is initially adjacent to a parking space, to move into the space it would need to move in a direction perpendicular to the allowed path of motion of the rear wheels.
The admissible motions of the car in its configuration space are an example of a nonholonomic system.
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