guava/src/com/google/common/collect/FluentIterable.java
@Beta
  public final FluentIterable<E> append(Iterable<? extends E> other) {
    return FluentIterable.concat(getDelegate(), other);
  }
@Beta
  public final FluentIterable<E> append(Iterable<? extends E> other) {
    return FluentIterable.concat(getDelegate(), other);
  }
Returns a fluent iterable whose iterators traverse first the elements of this fluent iterable,
followed by those of {@code other}. The iterators are not polled until necessary.

<p>The returned iterable's {@code Iterator} supports {@code remove()} when the corresponding
{@code Iterator} supports it.

<p><b>{@code Stream} equivalent:</b> {@link Stream#concat}.

@since 18.0