static <A extends IF0<Either<Iterable<A>, B>>, B> JTree jDynamicEitherTree(A root, O... _) {
  ret jDynamicTree(
    (Either<A, B>) (Either) eitherA(root),
    x -> {
      if (!isEitherA(x)) null; // leaves have no children
      Either<Iterable<A>, B> result = eitherAOpt(x)!;
      ret (Cl<Either<A, B>>)
        (isEitherA(result) ? map eitherA(eitherGetA(result)) : ll(eitherBOpt(result)));
    }, _);
}