THREE OBSERVERS SEE EVENT HORIZONS FROM SIMULTANEOUS EVENTS
NOT ONLY CAN THEY DETERMINE WHICH CAME FIRST, THEY CAN ALSO DETERMINE THE PLACE AND TIME OF ORIGIN.
( related to an established fixed-interval time and an established fixed-point space coordination system.)
It is only necessary to show that this determination of EVENT sequence is possible; if this can be done, then the sequencing or simultaneity of two EVENTS is a trivial matter. Therefore, the three observers will only require a single event to illustrate this point.