The metrisability of precompact sets

Metrisability of Unions of Spaces

Precompact Apartness Spaces

We present a notion of precompactness, and study some of its properties, in the context of apartness spaces whose apartness structure is not necessarily induced by any uniform one. The presentation lies entirely with a Bishop-style constructive framework, and is a contribution to the ongoing development of the constructive theories of apartness and uniformity.

Partial metrisability of continuous posets

In this article, we characterise all continuous posets which are partially metrizable in their Scott topology. We present conditions for pmetrizability, which are both necessary and sufficient, in terms of measurements, domain-theoretic bases and, in a more general setting, in terms of radially convex metrics. These conditions, together with their refinements and generalisations, set a natural ...

THE GROUP Aut(μ) IS ROELCKE PRECOMPACT

Following a similar result of Uspenskij on the unitary group of a separable Hilbert space we show that with respect to the lower (or Roelcke) uniform structure the Polish group G = Aut(μ), of automorphisms of an atomless standard Borel probability space (X,μ), is precompact. We identify the corresponding compactification as the space of Markov operators on L2(μ) and deduce that the algebra of r...

Metrisability of Two-dimensional Projective Structures

We carry out the programme of R. Liouville [18] to construct an explicit local obstruction to the existence of a Levi–Civita connection within a given projective structure [Γ] on a surface. The obstruction is of order 5 in the components of a connection in a projective class. It can be expressed as a point invariant for a second order ODE whose integral curves are the geodesics of [Γ] or as a w...