FluentIterable.from(input).transformAndConcat(new RepeatedStringValueOfFunction());
    assertEquals(asList("1", "1", "2", "2", "3", "3"), Lists.newArrayList(result));
  }

  private static final class RepeatedStringValueOfWildcardFunction
      implements Function<Integer, List<? extends String>> {
    @Override
    public List<String> apply(Integer from) {
      String value = String.valueOf(from);