The event-particles occupying a point-track have an order derived from the covering moments of any time-system. Those on a null-track have an order derived from routes which it is not necessary to discuss.
[43. Parallelism]. 43.1 A theory of parallelism holds for point-tracks and can be connected with the analogous theory for rects. Point-tracks which are points in the space of the same time-system are called 'parallel.' Thus a complete family of parallel point-tracks is merely a complete family of points in the space of some time-system. The parallelism of point-tracks is evidently transitive, symmetrical and reflexive. The definition of the parallelism of stations is derived from that of point-tracks.
[43.2] The parallelism of point-tracks and the parallelism of rects and moments are interconnected. Let
be any rect in a moment
, and let
be any family of parallel point-tracks. Then a certain set of point-tracks belonging to