proposition: Lemma in_filter_from {I T : Type} (D : set I) (B : I -> set T) (i : I) : D i -> filter_from D B (B i).
proof: Proof. by exists i. Qed.
imports: HB(structures) mathcomp(all_ssreflect all_algebra finmap generic_quotient) mathcomp(boolp classical_sets functions) mathcomp(cardinality mathcomp_extra fsbigop) reals signed