//
            // We need an executor that will not block.
            // We can't use work stealing, as we are building a graph
            // and this could lead to cycles where a thread waits for
            // a task to finish, then execute another one which waits
            // for the initial task...
            // In order to work around that problem, we override the

              }

              /*
               * The current set in sorted order looks like
               * {firstSetBit, firstSetBit + 1, ..., bitToFlip - 1, ...}
               * where it does *not* contain bitToFlip.
               *
               * The next combination is
               *
               * {0, 1, ..., bitToFlip - firstSetBit - 2, bitToFlip, ...}
               *

   * sorting all elements at once.
   *
   * <p>Retrieving a single element takes approximately O(log(M)) time, where M is the number of
   * iterators. (Retrieving all elements takes approximately O(N*log(M)) time, where N is the total
   * number of elements.)
   */
  private static class MergingIterator<T extends @Nullable Object> extends UnmodifiableIterator<T> {

    public int hashCode() {
      return map.hashCode();
    }

    private static final long serialVersionUID = 7845222491160860175L;
  }

  /**
   * Returns a view of a multimap where each value is transformed by a function. All other
   * properties of the multimap, such as iteration order, are left intact. For example, the code:
   *
   * <pre>{@code
   * Multimap<String, Integer> multimap =