HOW TO MOVE A CHAIR THROUGH A DOOR.

The author defines the door-width of a simple polygon (a 'chair') and give an O(n**2) algorithm for computing its door-width. It is first shown that all passages of the chair through the door can be reduced to a sequence of certain elementary motions. The author introduces the technique of constraint analysis in characterizing elementary motions. The algorithm actually constructs a motion of the chair through a door, and thus is a 'local expert' for planning motion through doors. Such algorithms have applications in more general motion-planning systems in robotics.