return parent.listIterator(index);
    }

    @Override
    public Map<String, Object> remove(final int index) {
        return parent.remove(index);
    }

    @Override
    public boolean remove(final Object o) {
        return parent.remove(o);
    }

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

  @Override
  public @Nullable V remove(@Nullable Object rowKey, @Nullable Object columnKey) {
    if ((rowKey == null) || (columnKey == null)) {
      return null;
    }
    Map<C, V> map = safeGet(backingMap, rowKey);
    if (map == null) {
      return null;
    }
    V value = map.remove(columnKey);
    if (map.isEmpty()) {
      backingMap.remove(rowKey);
    }
    return value;
  }

    assertFalse(entrySet.remove(immutableEntry(10, 'X')));
    assertTrue(entrySet.remove(immutableEntry(20, 'X')));
    assertFalse(entrySet.remove(immutableEntry(15, 'X')));
    entrySet = row.entrySet();
    assertTrue(entrySet.remove(immutableEntry(10, 'X')));
    assertFalse(entrySet.remove(immutableEntry(20, 'X')));
    assertFalse(entrySet.remove(immutableEntry(15, 'X')));
  }

    runConcurrentlyMutatedTest(elements(), ops(add(1), remove()), wrap);

    runConcurrentlyMutatedTest(elements(), ops(nop(), add(1)), wrap);

    runConcurrentlyMutatedTest(elements(1), ops(remove(), nop()), wrap);

    runConcurrentlyMutatedTest(elements(1), ops(remove(), add(2)), wrap);

    runConcurrentlyMutatedTest(elements(1, 2), ops(remove(), remove()), wrap);

    }
  }

  private static Set<Feature<?>> computeReserializedCollectionFeatures(Set<Feature<?>> features) {
    Set<Feature<?>> derivedFeatures = new HashSet<>(features);
    derivedFeatures.remove(SERIALIZABLE);
    derivedFeatures.remove(SERIALIZABLE_INCLUDING_VIEWS);
    return derivedFeatures;
  }

     * @param o
     *            object to be removed from this set, if present.
     * @return true if the set contained the specified element.
     */
    @Override
    public boolean remove(final Object o) {
        return map.remove(o) == PRESENT;
    }

    /**
     * Removes all of the elements from this set.
     */
    @Override
    public void clear() {
        map.clear();
    }

        list.addLast("1");
        list.addLast("2");
        assertThat(list.remove("3"), is(not(true)));
        assertThat(list.remove("1"), is(true));
        assertThat(list.remove(null), is(true));
        list.clear();
        list.addLast("1");
        list.addLast("2");
        list.addLast("3");
        list.remove(1);
        assertThat(list.get(0), is("1"));
        assertThat(list.get(1), is("3"));

    assertTrue(cycle.hasNext());
    assertThrows(IllegalStateException.class, () -> cycle.remove());
  }

  public void testCycleRemoveSameElementTwice() {
    Iterator<String> cycle = Iterators.cycle("a", "b");
    cycle.next();
    cycle.remove();
    assertThrows(IllegalStateException.class, () -> cycle.remove());
  }

  public void testCycleWhenRemoveIsNotSupported() {

        Long transferred;
        synchronized (transfers) {
            transferred = transfers.remove(transferEvent.getResource());
        }
        if (transferred != null) {
            event.setTransferredBytes(transferred);
        }

        synchronized (artifacts) {
            artifacts.remove(transferEvent.getResource());
        }

        listener.transferCompleted(event);
    }

    @Override

    public MetadataGraph removeVertex(MetadataGraphVertex v) {
        if (vertices != null && v != null) {
            vertices.remove(v);
        }

        if (incidentEdges != null) {
            incidentEdges.remove(v);
        }

        if (excidentEdges != null) {
            excidentEdges.remove(v);
        }

        return this;
    }