proposition: Lemma covered_bySr C P P' : (forall I D A, P I D A -> P' I D A) -> covered_by C P `<=` covered_by C P'.
proof: Proof. by move=> PP' X [I [D [A [CX PX ->]]]]; exists I, D, A; split=> //; apply: PP'. Qed.
imports: mathcomp(all_ssreflect all_algebra finmap) mathcomp(mathcomp_extra boolp classical_sets functions) mathcomp(cardinality fsbigop ) reals ereal signed topology normedtype sequences esum numfun HB(structures)