زیرپایه (توپولوژی)

In topology in mathematics, a subbase (or subbasis, prebase, prebasis) for the topology of a topological space is a subcollection B of \tau that generates \tau, in the sense that \tau is the smallest topology containing B as open sets. A slightly different definition is used by some authors, and there are other useful equivalent formulations of the definition; these are discussed below.