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The following statements hold generally: Every physical

description resolves itself into a number of statements, each of

which refers to the space-time coincidence of two events A and B.

In terms of Gaussian co-ordinates, every such statement is

expressed by the agreement of their four co-ordinates x1, x2, x3,

x4. Thus in reality, the description of the time-space continuum

by means of Gauss co-ordinates completely replaces the

description with the aid of a body of reference, without

suffering from the defects of the latter mode of description; it

is not tied down to the Euclidean character of the continuum

which has to be represented.

XXVIII.

EXACT FORMULATION OF THE GENERAL PRINCIPLE OF RELATIVITY