# Definition of the boolean combination

Recently I have found such a thing like ,,finite boolean combination of open sets" (of a topological space). Unfortunatlety I haven't found anywhere the precise definition of such combination.

Does anyone know where could I find it? The only thing that I can figure out myself is connected with the boolean algebra of sets where we have three operations: union, intersection and complement of sets. Is this combination a set that we can get using intersections (of two sets), unions (also of two sets) and complement operations applied finitely many times to the mentioned family of open sets? Am I right?

• It seems you are right, except that those unions and intersections are not necessarily of two sets, but finitely many (which is equivalent since you can make the union/intersection of $n$ sets by making $n-1$ times that operation on two sets). – amrsa Jan 4 '17 at 10:04