Function: asin
Section: transcendental
C-Name: gasin
Prototype: Gp
Help: asin(x): inverse sine of x.
Doc: principal branch of $\text{sin}^{-1}(x)$, i.e.~such
 that $\text{Re(asin}(x))\in [-\pi/2,\pi/2]$. If $x\in \R$ and $|x|>1$ then
 $\text{asin}(x)$ is complex.
