*/
  Collection<V> get(@ParametricNullness K key);

  /**
   * Returns a view collection of all <i>distinct</i> keys contained in this multimap. Note that the
   * key set contains a key if and only if this multimap maps that key to at least one value.
   *
   * <p>Changes to the returned set will update the underlying multimap, and vice versa. However,

   * <i>adding</i> to the returned set is not possible.
   */
  @Override
  public Set<K> keySet() {
    return super.keySet();
  }

  /**
   * Returns a collection of all values in the multimap. Changes to the returned collection will
   * update the underlying multimap, and vice versa.
   *

  /*
   * We have some considerable complexity in these create methods because of
   * Builder.buildKeepingLast(). The same Builder might be called with buildKeepingLast() and then
   * buildOrThrow(), or vice versa. So in particular, if we modify alternatingKeysAndValues to
   * eliminate duplicate keys (for buildKeepingLast()) then we have to ensure that a later call to

      Sets.newSetFromMap(map);
      fail();
    } catch (IllegalArgumentException expected) {
    }
  }

  /** The 0-ary cartesian product is a single empty list. */
  public void testCartesianProduct_zeroary() {
    assertThat(Sets.cartesianProduct()).containsExactly(list());
  }

  /** A unary cartesian product is one list of size 1 for each element in the input set. */
  public void testCartesianProduct_unary() {

   * Returns 1 if {@code x < y} as unsigned longs, and 0 otherwise. Assumes that x - y fits into a
   * signed long. The implementation is branch-free, and benchmarks suggest it is measurably faster
   * than the straightforward ternary expression.
   */
  @VisibleForTesting
  static int lessThanBranchFree(long x, long y) {
    // Returns the sign bit of x - y.
    return (int) (~~(x - y) >>> (Long.SIZE - 1));
  }

  /**

   *       instances.
   *   <li>For the constructor or static factory method used to construct instances, it's checked
   *       that when equal parameters are passed, the result instance should also be equal; and vice
   *       versa.
   *   <li>If a non-private constructor or non-private static factory method exists:
   *       <ul>
   *         <li>Test will fail if default value for a parameter cannot be determined.

    // being selected in phase 1
    Preconditions.checkState(boxedBoolean, "", (Object) boxedLong);

    // ternaries introduce their own problems. because of the ternary (which requires a boxing
    // operation) no overload can be selected in phase 1.  and in phase 2 it is ambiguous since it
    // matches with the second parameter being boxed and without it being boxed.  The cast to Object

            if (!successors.hasNext()) {
              return next;
            }
            horizon.addFirst(successors);
            ancestorStack.push(next);
          }
          // TODO(b/192579700): Use a ternary once it no longer confuses our nullness checker.
          if (!ancestorStack.isEmpty()) {
            return ancestorStack.pop();
          }
          return endOfData();
        }
      };
    }

   * a signed int. The implementation is branch-free, and benchmarks suggest it is measurably (if
   * narrowly) faster than the straightforward ternary expression.
   */
  @VisibleForTesting
  static int lessThanBranchFree(int x, int y) {
    // The double negation is optimized away by normal Java, but is necessary for GWT

      if (leftChildIndex < 0) {
        return -1;
      }
      return findMin(getLeftChildIndex(leftChildIndex), 4);
    }

    /**
     * Moves an element one level up from a min level to a max level (or vice versa). Returns the
     * new position of the element.
     */
    int crossOverUp(int index, E x) {
      if (index == 0) {
        queue[0] = x;
        return 0;
      }