There is only one way to do this.

Note that if we vary the time and take times with the same three space co-ordinates, then the event-particles, thus indicated, are all at the same point.

But seeing that there is nothing else except the event-particles, this can only mean that the point (p_1, p_2, p_3) of the space in the p-system is merely the collection of event-particles (p_1, p_2, p_3, [p_4]), where p_4 is varied and (p_1, p_2, p_3) is kept fixed.

It is rather disconcerting to find that a point in space is not a simple entity; but it is a conclusion which follows immediately from the relative theory of space.
Furthermore the inhabitant of Mars determines event-particles by another system of measurements.

Call his system the q-system.