@Override
        protected Set<K> delegate() {
          return delegate.keySet();
        }

        @Override
        public Iterator<K> iterator() {
          return Iterators.unmodifiableIterator(delegate.keySet().iterator());
        }

        @Override
        public boolean removeAll(Collection<?> c) {
          return delegate.keySet().removeAll(c);
        }

        @Override

  @Override
  int indexOf(@Nullable Object target) {
    return -1;
  }

  @Override
  public UnmodifiableIterator<C> iterator() {
    return emptyIterator();
  }

  @GwtIncompatible // NavigableSet
  @Override
  public UnmodifiableIterator<C> descendingIterator() {
    return emptyIterator();
  }

  @Override
  boolean isPartialView() {
    return false;
  }

      return super.writeReplace();
    }

    @GwtIncompatible @J2ktIncompatible private static final long serialVersionUID = 0;
  }

  @Override
  UnmodifiableIterator<Entry<K, V>> entryIterator() {
    return new UnmodifiableIterator<Entry<K, V>>() {
      final Iterator<? extends Entry<K, ? extends ImmutableCollection<V>>> asMapItr =
          map.entrySet().iterator();
      @Nullable K currentKey = null;

import static com.google.common.graph.GraphConstants.NOT_AVAILABLE_ON_UNDIRECTED;

import com.google.common.annotations.Beta;
import com.google.common.collect.Iterators;
import com.google.common.collect.UnmodifiableIterator;
import com.google.errorprone.annotations.Immutable;
import java.util.Objects;
import org.jspecify.annotations.Nullable;

/**

  private final E element;

  SingletonImmutableSet(E element) {
    this.element = checkNotNull(element);
  }

  @Override
  public int size() {
    return 1;
  }

  @Override
  public UnmodifiableIterator<E> iterator() {
    return Iterators.singletonIterator(element);
  }

  @Override
  public boolean contains(@Nullable Object object) {
    return element.equals(object);
  }

import static com.google.common.graph.GraphConstants.NOT_AVAILABLE_ON_UNDIRECTED;

import com.google.common.annotations.Beta;
import com.google.common.collect.Iterators;
import com.google.common.collect.UnmodifiableIterator;
import com.google.errorprone.annotations.Immutable;
import java.util.Objects;
import org.jspecify.annotations.Nullable;

/**

 *
 * @since 7.0
 * @author Louis Wasserman
 */
@GwtCompatible
public abstract class UnmodifiableListIterator<E extends @Nullable Object>
    extends UnmodifiableIterator<E> implements ListIterator<E> {
  /** Constructor for use by subclasses. */
  protected UnmodifiableListIterator() {}

  /**
   * Guaranteed to throw an exception and leave the underlying data unmodified.
   *

  ImmutableMapKeySet(ImmutableMap<K, V> map) {
    this.map = map;
  }

  @Override
  public int size() {
    return map.size();
  }

  @Override
  public UnmodifiableIterator<K> iterator() {
    return map.keyIterator();
  }

  @Override
  public boolean contains(@Nullable Object object) {
    return map.containsKey(object);
  }

  @Override
  K get(int index) {

  }

  @Override
  public int size() {
    return 1;
  }

  @Override
  public boolean contains(@Nullable Object target) {
    return element.equals(target);
  }

  @Override
  public UnmodifiableIterator<E> iterator() {
    return singletonIterator(element);
  }

  @Override
  public ImmutableList<E> asList() {
    return ImmutableList.of(element);
  }

  @Override
  boolean isPartialView() {

 *       }
 *     };
 * }
 *
 * @author Chris Povirk
 * @since 12.0 (in Guava as {@code AbstractLinkedIterator} since 8.0)
 */
@GwtCompatible
public abstract class AbstractSequentialIterator<T> extends UnmodifiableIterator<T> {
  private @Nullable T nextOrNull;

  /**
   * Creates a new iterator with the given first element, or, if {@code firstOrNull} is null,
   * creates a new empty iterator.
   */