Geometric random graphs and Rado sets of continuous functions

Abstract

We prove the existence of Rado sets in the Banach space of continuous functions on [0,1]. A countable dense set S is Rado if with probability 1, the infinite geometric random graph on S, formed by probabilistically making adjacent elements of S that are within unit distance of each other, is unique up to isomorphism. We show that for a suitable measure which we construct, almost all countable dense sets in the subspaces of piecewise linear functions and of polynomials are Rado. Moreover, all graphs arising from such sets are of a unique isomorphism type. For the subspace of Brownian motion paths, almost all countable subsets are Rado (for a suitable measure) and the resulting graphs are of a unique isomorphism type. We show that the graph arising from piecewise linear functions and polynomials is not isomorphic to the graph arising from Brownian motion paths. Moreover, these graphs are non-isomorphic to graphs arising from Rado sets in $\mathbb{R}^n$, or the sequence spaces $c$ and $c_0$.