checkNotNull(iterable);
    Iterators.checkNonnegative(position);
    if (iterable instanceof List) {
      List<? extends T> list = Lists.cast(iterable);
      return (position < list.size()) ? list.get(position) : defaultValue;
    } else {
      Iterator<? extends T> iterator = iterable.iterator();
      Iterators.advance(iterator, position);
      return Iterators.getNext(iterator, defaultValue);
    }
  }

        @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
      public Iterator<T> iterator() {
        return Iterators.concat(
            /* lazily generate the iterators on each input only as needed */
            new AbstractIndexedListIterator<Iterator<? extends T>>(inputs.length) {
              @Override
              public Iterator<? extends T> get(int i) {
                return inputs[i].iterator();
              }
            });
      }

      }
    };
  }

  @Override
  public Iterator<EndpointPair<N>> incidentEdgeIterator(N thisNode) {
    checkNotNull(thisNode);

    Iterator<EndpointPair<N>> resultWithDoubleSelfLoop;
    if (orderedNodeConnections == null) {
      resultWithDoubleSelfLoop =
          Iterators.concat(
              Iterators.transform(
                  predecessors().iterator(),

        @Override
        public @Nullable Object execute(Iterator<?> iterator) {
          iterator.remove();
          return null;
        }
      };

  private static final IteratorOperation NEXT_METHOD =
      new IteratorOperation() {
        @Override
        public @Nullable Object execute(Iterator<?> iterator) {
          return iterator.next();
        }
      };

  public void testCopyOf_iterator_oneElementRepeated() {
    Iterator<String> iterator = Iterators.forArray("a", "a", "a");
    Set<String> set = copyOf(iterator);
    assertEquals(singleton("a"), set);
  }

  public void testCopyOf_iterator_general() {
    Iterator<String> iterator = Iterators.forArray("a", "b", "a");
    Set<String> set = copyOf(iterator);
    assertEquals(2, set.size());
    assertTrue(set.contains("a"));

      }

      @Override
      Iterator<E> elementIterator() {
        throw new AssertionError("should never be called");
      }

      @Override
      Iterator<Entry<E>> entryIterator() {
        final Iterator<? extends Entry<? extends E>> iterator1 = multiset1.entrySet().iterator();
        final Iterator<? extends Entry<? extends E>> iterator2 = multiset2.entrySet().iterator();

      }

      @Override
      Iterator<E> elementIterator() {
        throw new AssertionError("should never be called");
      }

      @Override
      Iterator<Entry<E>> entryIterator() {
        final Iterator<? extends Entry<? extends E>> iterator1 = multiset1.entrySet().iterator();
        final Iterator<? extends Entry<? extends E>> iterator2 = multiset2.entrySet().iterator();

        @Override
        public @Nullable Object execute(Iterator<?> iterator) {
          iterator.remove();
          return null;
        }
      };

  private static final IteratorOperation NEXT_METHOD =
      new IteratorOperation() {
        @Override
        public @Nullable Object execute(Iterator<?> iterator) {
          return iterator.next();
        }
      };

    }
  }

  /**
   * Verifies that an Iterator is unmodifiable.
   *
   * <p>This test only works with iterators that iterate over a finite set.
   */
  public static void assertIteratorIsUnmodifiable(Iterator<?> iterator) {
    while (iterator.hasNext()) {
      iterator.next();
      try {
        iterator.remove();
        fail("Remove on unmodifiable iterator succeeded");