There are presumably three ways of characterizing the abstract Euclidean space $E^n$ that are quite different in spirit:
- axiomatically (with axioms concerning dimension)
- by the abstract Euclidean group $E(n)$ (as its symmetry group, determining $E^n$ uniquely)
- by presupposing a metric and requiring that the space is a maximal one with respect to the property that the $(n+1)$-dimensional Cayley-Menger determinant vanishes for all $(n+2)$-tuples of points and does not vanish for all $k$-tuples of points "in general position" for $k < n+2$.
[Having tried to "rescue" 3 by adding conditions in italics, due to Robin's comment.]
Question 1: Is it correct, actually, that $E^n$ is uniquely determined via 2 and 3?
Question 2: What are other ways of characterizing $E^n$ that are quite different in spirit?