NOTES
The saddle-shape of the Ringworld's inner surface makes navigation on that surface startlingly different than navigation on earth. Motion "north" and "south" across the Ring is much like motion over the surface of the Earth; the direction of "gravity" converges towards a point under the Ring. Motion "spinward" and "antispinward" is different - because the direction of "gravity" diverges, and as we shall see, that makes a big difference.