@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