\int^1_\kappa \left[\bigl(1-w^2\bigr)\bigl(\kappa^2-w^2\bigr)\right]^{-1/2} dw = \frac{4}{\left(1+\sqrt{\kappa}\,\right)^2} K \left(\left(\frac{1-\sqrt{\kappa}}{1+\sqrt{\kappa}}\right)^{\!\!2}\right)