\int_{\frac{-1}{2}}^0 \sqrt{1+\left(\frac{d}{d x}\sqrt{\frac{1}{4}-x^2}\right)^2} \, dx\leq \ell \leq \lim_{e\to 0} \int_{-\left(\frac{1 }{2}+e\right)}^0 \sqrt{1+\left(\frac{d}{d x}\sqrt{\left(\frac{1}{2}+e\right)^2-x^2}\right)^2} \, dx