@ParametricNullness
    V rightValue();

    /**
     * Two instances are considered equal if their {@link #leftValue()} values are equal and their
     * {@link #rightValue()} values are also equal.
     */
    @Override
    boolean equals(@Nullable Object other);

    /**
     * The hash code equals the value {@code Arrays.asList(leftValue(), rightValue()).hashCode()}.
     */
    @Override

    @ParametricNullness
    V rightValue();

    /**
     * Two instances are considered equal if their {@link #leftValue()} values are equal and their
     * {@link #rightValue()} values are also equal.
     */
    @Override
    boolean equals(@Nullable Object other);

    /**
     * The hash code equals the value {@code Arrays.asList(leftValue(), rightValue()).hashCode()}.
     */
    @Override

         * further about this.
         */
        V rightValue = uncheckedCastNullableTToT(onlyOnRight.remove(leftKey));
        if (valueEquivalence.equivalent(leftValue, rightValue)) {
          onBoth.put(leftKey, leftValue);
        } else {
          differences.put(leftKey, ValueDifferenceImpl.create(leftValue, rightValue));
        }
      } else {
        onlyOnLeft.put(leftKey, leftValue);
      }

         * further about this.
         */
        V rightValue = uncheckedCastNullableTToT(onlyOnRight.remove(leftKey));
        if (valueEquivalence.equivalent(leftValue, rightValue)) {
          onBoth.put(leftKey, leftValue);
        } else {
          differences.put(leftKey, ValueDifferenceImpl.create(leftValue, rightValue));
        }
      } else {
        onlyOnLeft.put(leftKey, leftValue);
      }