and is based solely on the fundamental time-order
at
. Thus the time-order at
is extended as a time-order for all events at all places.
11.3 There are questions which require elucidation before this definition can be understood. What is a place? We have chosen a vague term on purpose, so as to postpone its consideration until now. A place can only be marked by phenomena capable of recognition, for example the continued appearance of a material body. Thus we must construe