fact: Definition continuous_at (T U : nbhsType) (x : T) (f : T -> U) := (f%function @ x --> f%function x).
imports: HB(structures) mathcomp(all_ssreflect all_algebra finmap generic_quotient) mathcomp(boolp classical_sets functions) mathcomp(cardinality mathcomp_extra fsbigop) reals signed