The value of \( \displaystyle \lim_{x \to 0^+} \frac{\cos^{-1}(x - [x^2]) - \sin^{-1}(x - [x^2])}{x - x^3} \), where \( [x] \) denotes the greatest integer \( \le x \) is:
\( \pi \)
\( \tfrac{\pi}{4} \)
\( 0 \)
\( \tfrac{\pi}{2} \)