/**
   * Returns a fluent iterable that combines two iterables. The returned iterable has an iterator
   * that traverses the elements in {@code a}, followed by the elements in {@code b}. 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>{@code Stream} equivalent:</b> {@link Stream#concat}.

  /**
   * Returns a fluent iterable that combines two iterables. The returned iterable has an iterator
   * that traverses the elements in {@code a}, followed by the elements in {@code b}. 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>{@code Stream} equivalent:</b> {@link Stream#concat}.

  }

  /**
   * Combines two 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}. The source
   * iterators are not polled until necessary.
   *
   * <p>The returned iterable's iterator supports {@code remove()} when the corresponding input
   * iterator supports it.
   *

  }

  /**
   * Combines two 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}. The source
   * iterators are not polled until necessary.
   *
   * <p>The returned iterable's iterator supports {@code remove()} when the corresponding input
   * iterator supports it.
   *

    };
  }

  /**
   * Combines two iterators into a single iterator. The returned iterator iterates across the
   * elements in {@code a}, followed by the elements in {@code b}. The source iterators are not
   * polled until necessary.
   *
   * <p>The returned iterator supports {@code remove()} when the corresponding input iterator
   * supports it.
   */
  public static <T extends @Nullable Object> Iterator<T> concat(