fact: Definition accessible_space := forall x y, x != y -> exists A : set T, open A /\ x \in A /\ y \in ~` A.
imports: HB(structures) mathcomp(all_ssreflect all_algebra finmap generic_quotient) mathcomp(boolp classical_sets functions) mathcomp(cardinality mathcomp_extra fsbigop) reals signed