fact: Definition basis (B : set (set T)) := B `<=` open /\ forall x, filter_from [set U | B U /\ U x] id --> x.
imports: HB(structures) mathcomp(all_ssreflect all_algebra finmap generic_quotient) mathcomp(boolp classical_sets functions) mathcomp(cardinality mathcomp_extra fsbigop) reals signed