if (o instanceof Cell) {
        Cell<?, ?, ?> cell = (Cell<?, ?, ?>) o;
        Map<C, V> row = safeGet(rowMap(), cell.getRowKey());
        return row != null
            && Collections2.safeContains(
                row.entrySet(), immutableEntry(cell.getColumnKey(), cell.getValue()));
      }
      return false;
    }

    @Override
    public boolean remove(@Nullable Object o) {

      if (o instanceof Cell) {
        Cell<?, ?, ?> cell = (Cell<?, ?, ?>) o;
        Map<C, V> row = safeGet(rowMap(), cell.getRowKey());
        return row != null
            && Collections2.safeContains(
                row.entrySet(), immutableEntry(cell.getColumnKey(), cell.getValue()));
      }
      return false;
    }

    @Override
    public boolean remove(@Nullable Object o) {

      }

      // The following methods are included for performance.

      @Override
      public boolean contains(@Nullable Object o) {
        return Collections2.safeContains(submap.entrySet(), o);
      }

      @Override
      public boolean remove(@Nullable Object o) {
        if (!contains(o)) {
          return false;
        }

   */
  public static boolean contains(Iterable<?> iterable, @Nullable Object element) {
    if (iterable instanceof Collection) {
      Collection<?> collection = (Collection<?>) iterable;
      return Collections2.safeContains(collection, element);
    }
    return Iterators.contains(iterable.iterator(), element);
  }

  /**
   * Removes, from an iterable, every element that belongs to the provided collection.
   *

    @Override
    public boolean containsKey(@Nullable Object key) {
      return backingSet().contains(key);
    }

    @Override
    public @Nullable V get(@Nullable Object key) {
      if (Collections2.safeContains(backingSet(), key)) {
        @SuppressWarnings("unchecked") // unsafe, but Javadoc warns about it
        K k = (K) key;
        return function.apply(k);
      } else {
        return null;
      }
    }

      return getOrDefault(key, null);
    }

    @Override
    public @Nullable V getOrDefault(@Nullable Object key, @Nullable V defaultValue) {
      if (Collections2.safeContains(backingSet(), key)) {
        @SuppressWarnings("unchecked") // unsafe, but Javadoc warns about it
        K k = (K) key;
        return function.apply(k);
      } else {
        return defaultValue;
      }