High Quality Content by WIKIPEDIA articles! In mathematics, a porosity is a concept in the study of metric spaces. Like the concepts of meagre and measure zero sets, porosity is a notion of a set being somehow "sparse" or "lacking bulk"; however, porosity is not equivalent to either of the above notions, as shown below.Let (X, d) be a complete metric space and let E be a subset of X. Let B(x, r) denote the closed ball in (X, d) with centre x ? X and radius r > 0A subset of X is called ?-porous if it is a countable union of porous subsets of X.

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