The moving sofa constant C41a=A is the maximum area of a connected, rigid planar shape that can maneuver through an L-shaped corridor of unit width.
The corridor is formed by two semi-infinite strips of width 1 meeting at a right angle.
The problem asks for the shape of the largest area (the "sofa") that can be moved from one end of the corridor to the other by a continuous rigid motion (translation and rotation).