code: public static <T> Iterable<T> concat(
        Iterable<? extends T> a, Iterable<? extends T> b, Iterable<? extends T> c) {
      return FluentIterable.concat(a, b, c);
    }
docs: Combines three iterables into a single iterable. The returned iterable has an iterator that
  traverses the elements in {@code a}, followed by the elements in {@code b}, followed by the
  elements in {@code c}. The source iterators are not polled until necessary.
  
  <p>The returned iterable's iterator supports {@code remove()} when the corresponding input
  iterator supports it.
  
  <p><b>Java 8 users:</b> The {@code Stream} equivalent of this method is {@code
  Streams.concat(a, b, c)}.