@Override
    public String toString() {
        if (Left != null && Right != null)
            return MessageFormat.format("{0} {1} {2}", Left, Verb, Right);

        if (LeftDual != null && Right != null)
            return MessageFormat.format("{0} {1} {2}", LeftDual, Verb, Right);

        if (Left != null && RightDual != null)
            return MessageFormat.format("{0} {1} {2}", Left, Verb, RightDual);

        else if (LeftDual != null && RightDual != null)
            return MessageFormat.format("{0} {1} {2}", LeftDual, Verb, RightDual);

        return null;
    }