For every analytic function $f$ on $G$ (simply connected,open) s.t $f(z) \neq 0, \forall z \in G$, then $\exists$ g analytic in $G$ s.t $g^2 = f$
Does there exist a holomorphic function $\varphi(z)$ such that $\varphi^2(z) = \psi(z)$