docs: public static <K, V, V2> Lens.Simple<Map<K, V>, Map<K, V2>> mappingValues(Iso<V, V, V2, V2> iso) {
          return simpleLens(m -> toMap(HashMap::new, map(t -> t.biMapR(view(iso)), map(Tuple2::fromEntry, m.entrySet()))),
                            (s, b) -> view(mappingValues(iso.mirror()), b));
      }