 The rooms and the solution line must all be drawn on a single side of a normal flat sheet of paper.The solution line must be continuous, but can bend sharply or smoothly in any way and can even cross over itself (but not at a wall, so this is often prohibited).The solution line must cross over each "wall" exactly once, where "cross over" means to pass completely from one to the other of the two rooms that are separated by the "wall", or from a room to the area outside the drawing.