Let (X,G,f) be a topological
transformation group. Suppose that the phase space X is compact, separable metric,
and locally contractible and the group G is the additive group of all real numbers R
with the usual topology. If X is a minimal set of dimL(X) ≦ 2 then X is a manifold,
imposing a further condition on the action when dimL(X) = 2. Hence X is a
singleton, a circle or a torus according to its dimension.