Biocaml 0.4-dev : Biocaml_genomeMap.Make.Selection.union

let union u v =

   let keys = List.dedup (Map.keys u @ Map.keys v) in

   List.fold keys ~init:Map.empty ~f:(fun accu k ->

     Map.add accu ~key:k ~data:(

      Biocaml_iset.union

       (Option.value (Map.find u k) ~default:Biocaml_iset.empty)

       (Option.value (Map.find v k) ~default:Biocaml_iset.empty)

     )

    )