The Lusternik–Schnirelmann category of metric spaces

We extend the theory of the Lusternik–Schnirelmann category to general metric spaces by means of covers by arbitrary subsets. We also generalize the definition of the strict category weight. We show that if the Bockstein homomorphism on a metric space X is non-zero, then cat X ⩾ 2 , and use this to compute the category of Pontryagin surfaces. Additionally, we prove that a Polish space with LS-category n can be presented as the inverse limit of ANR spaces of category at most n.