Definition:Inverse Hyperbolic Secant/Complex/Principal Branch

Definition
The principal branch of the complex inverse hyperbolic secant function is defined as:
 * $\forall z \in \C: \operatorname{Sech}^{-1} \left({z}\right) := \operatorname{Ln} \left({\dfrac {1 + \sqrt{1 - z^2} } z}\right)$

where:
 * $\operatorname{Ln}$ denotes the principal branch of the complex natural logarithm
 * $\sqrt{1 - z^2}$ denotes the principal square root of $1 - z^2$.

Also see

 * Derivation of Hyperbolic Arcsecant from Inverse Hyperbolic Secant Multifunction