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Rh occurrence, if space is of three dimensions. If there are more than four observers in the standard system the relations between all the different observations of an event will depend upon the nature of space, and will take a comparatively simple form if the space is Euclidean.

If the position and time associated with an object B is always determined from measurements by a number of standard observers $$A_{1},\dots A_{r}$$, so that a consistent universal time exists for each point of space, the following conclusion may be deduced by elementary geometry for Euclidean space:

If two observers B and C are at rest or in motion relative to the standard system, and their velocities are less than that of light, there is only one instant at which B is able to observe an instantaneous event experienced by C, but if one of the observers is moving with a velocity greater than that of light this is not necessarily the case; in fact it may happen that B sees two or more pictures of the same event.