proposition: Lemma cvg_at_left_filter : f z @[z --> x] --> f x -> f z @[z --> x^'-] --> f x.
proof: Proof. exact: (@cvg_within_filter _ _ _ (nbhs x)). Qed.
imports: HB(structures) mathcomp(all_ssreflect ssralg ssrint ssrnum finmap matrix) mathcomp(rat interval zmodp vector fieldext falgebra) mathcomp(mathcomp_extra boolp classical_sets functions) mathcomp(cardinality set_interval Rstruct) ereal reals signed topology prodnormedzmodule