Count frequency = backingMap.get(element);
    int oldCount;
    if (frequency == null) {
      oldCount = 0;
      backingMap.put(element, new Count(occurrences));
    } else {
      oldCount = frequency.get();
      long newCount = (long) oldCount + (long) occurrences;
      checkArgument(newCount <= Integer.MAX_VALUE, "too many occurrences: %s", newCount);

    checkNonnegative(count, "count");
    int oldCount = (count == 0) ? backingMap.remove(element) : backingMap.put(element, count);
    size += (count - oldCount);
    return oldCount;
  }

  @Override
  public final boolean setCount(@ParametricNullness E element, int oldCount, int newCount) {
    checkNonnegative(oldCount, "oldCount");
    checkNonnegative(newCount, "newCount");

  private void assertSetCountNegativeOldCount() {
    try {
      getMultiset().setCount(e3(), -1, 1);
      fail("calling setCount() with a negative oldCount should throw IllegalArgumentException");
    } catch (IllegalArgumentException expected) {
    }
  }

  // Negative oldCount.

  @CollectionFeature.Require(SUPPORTS_ADD)
  public void testSetCountConditional_negativeOldCount_addSupported() {
    assertSetCountNegativeOldCount();

  private void assertSetCountNegativeOldCount() {
    try {
      getMultiset().setCount(e3(), -1, 1);
      fail("calling setCount() with a negative oldCount should throw IllegalArgumentException");
    } catch (IllegalArgumentException expected) {
    }
  }

  // Negative oldCount.

  @CollectionFeature.Require(SUPPORTS_ADD)
  public void testSetCountConditional_negativeOldCount_addSupported() {
    assertSetCountNegativeOldCount();

    return delegate().setCount(element, count);
  }

  @CanIgnoreReturnValue
  @Override
  public boolean setCount(@ParametricNullness E element, int oldCount, int newCount) {
    return delegate().setCount(element, oldCount, newCount);
  }

  /**
   * A sensible definition of {@link #contains} in terms of {@link #count}. If you override {@link

      K k = (K) key;
      int oldCount = 0;
      Iterator<V> itr = collection.iterator();
      while (itr.hasNext()) {
        V v = itr.next();
        if (satisfies(k, v)) {
          oldCount++;
          if (oldCount <= occurrences) {
            itr.remove();
          }
        }
      }
      return oldCount;
    }

    @Override

    }

    @Override
    public int hashCode() {
      return standardHashCode();
    }

    @Override
    public boolean setCount(T element, int oldCount, int newCount) {
      return standardSetCount(element, oldCount, newCount);
    }

    @Override
    public int setCount(T element, int count) {
      return standardSetCount(element, count);
    }

    @Override

      Multiset<E> self, @ParametricNullness E element, int oldCount, int newCount) {
    checkNonnegative(oldCount, "oldCount");
    checkNonnegative(newCount, "newCount");

    if (self.count(element) == oldCount) {
      self.setCount(element, newCount);
      return true;
    } else {
      return false;
    }
  }

  static <E extends @Nullable Object> Iterator<E> elementIterator(

      Multiset<E> self, @ParametricNullness E element, int oldCount, int newCount) {
    checkNonnegative(oldCount, "oldCount");
    checkNonnegative(newCount, "newCount");

    if (self.count(element) == oldCount) {
      self.setCount(element, newCount);
      return true;
    } else {
      return false;
    }
  }

  static <E extends @Nullable Object> Iterator<E> elementIterator(

      K k = (K) key;
      int oldCount = 0;
      Iterator<V> itr = collection.iterator();
      while (itr.hasNext()) {
        V v = itr.next();
        if (satisfies(k, v)) {
          oldCount++;
          if (oldCount <= occurrences) {
            itr.remove();
          }
        }
      }
      return oldCount;
    }

    @Override