*   tf.optimizers => tf.keras.optimizers
    *   Add tf.keras.layers.AbstractRNNCell as the preferred implementation of
        RNN cell for TF v2. User can use it to implement RNN cell with custom
        behavior.
    *   Adding `clear_losses` API to be able to clear losses at the end of
        forward pass in a custom training loop in eager.

 * (unless there are {@link Double#NaN NaN} values, see below); otherwise, the result is the average
 * of the values which would appear at the indexes floor(x) and ceil(x) weighted by (1-frac(x)) and
 * frac(x) respectively. This is the same definition as used by Excel and by S, it is the Type 7
 * definition in <a

     *     {@link #whenAllComplete(Iterable)} or {@link #whenAllComplete(Iterable)}
     * @throws IllegalStateException if called outside of a call to {@link
     *     CombiningCallable#call(DeferredCloser, Peeker)} or {@link
     *     AsyncCombiningCallable#call(DeferredCloser, Peeker)}
     */
    @ParametricNullness
    public <D extends @Nullable Object> D getDone(ClosingFuture<D> closingFuture)

     * we must return it in the following next() call even if it was in the process of being removed
     * when hasNext() was called.
     */
    private @Nullable E nextItem;

    /**
     * Index of element returned by most recent call to next. Reset to -1 if this element is deleted
     * by a call to remove.
     */
    private int lastRet;

    Itr() {
      lastRet = -1;

   * skipped element by immediately calling {@code remove()} on the returned fluent iterable's
   * iterator, as the {@code Iterator} contract states that a call to {@code * remove()} before a
   * call to {@code next()} will throw an {@link IllegalStateException}.
   *
   * <p><b>{@code Stream} equivalent:</b> {@link Stream#skip} (same).
   */
  public final FluentIterable<E> skip(int numberToSkip) {

   * skipped element by immediately calling {@code remove()} on the returned fluent iterable's
   * iterator, as the {@code Iterator} contract states that a call to {@code * remove()} before a
   * call to {@code next()} will throw an {@link IllegalStateException}.
   *
   * <p><b>{@code Stream} equivalent:</b> {@link Stream#skip} (same).
   */
  public final FluentIterable<E> skip(int numberToSkip) {

     * we must return it in the following next() call even if it was in the process of being removed
     * when hasNext() was called.
     */
    private @Nullable E nextItem;

    /**
     * Index of element returned by most recent call to next. Reset to -1 if this element is deleted
     * by a call to remove.
     */
    private int lastRet;

    Itr() {
      lastRet = -1;

   * {@code iterator().remove()} of an unmodifiable list could throw either {@link
   * IllegalStateException} or {@link UnsupportedOperationException}. Note that iterator
   * implementations should always throw one of the exceptions in a {@code PermittedExceptions}
   * instance, since {@code PermittedExceptions} is thrown only when a method call is invalid.
   *

   * {@code iterator().remove()} of an unmodifiable list could throw either {@link
   * IllegalStateException} or {@link UnsupportedOperationException}. Note that iterator
   * implementations should always throw one of the exceptions in a {@code PermittedExceptions}
   * instance, since {@code PermittedExceptions} is thrown only when a method call is invalid.
   *

   * a later time.
   *
   * <p>Since this method uses {@code HashMap} instances internally, the keys of the supplied maps
   * must be well-behaved with respect to {@link Object#equals} and {@link Object#hashCode}.
   *
   * <p><b>Note:</b>If you only need to know whether two maps have the same mappings, call {@code
   * left.equals(right)} instead of this method.
   *
   * @param left the map to treat as the "left" map for purposes of comparison