Property of Baire
Difference of an open set by a meager set / From Wikipedia, the free encyclopedia
A subset of a topological space has the property of Baire (Baire property, named after René-Louis Baire), or is called an almost open set, if it differs from an open set by a meager set; that is, if there is an open set such that is meager (where denotes the symmetric difference).[1]