$$\sqrt{a-2a^{1/2}b^{1/2}+b}-\frac{a-b}{a^{1/2}-b^{1/2}}$$
$|\sqrt{a}-\sqrt{b}|-\sqrt{a}-\sqrt{b}$
$\frac{sign(\sqrt{a}-\sqrt{b})-1}{2\sqrt{a}}$
