 If the temporal interval between two events is 0, then we say that the two events are simultaneous. This relation of (absolute) simultaneity is an equivalence relation (That is, it is reflexive, symmetric, and transitive.) that slices (partitions or foliates) the spacetime or manifold into mutually exclusive and exhaustive planes of simultaneity. These planes of simultaneity can then be completely ordered by the relation ‘is earlier than’ or its converse ‘is later than’.