Definition:Doubly Periodic Function

Definition
Let $f: \C \to \C$ be a complex function.

Then $f$ is a doubly-periodic function there exist $\omega_1, \omega_2 \in \C$ such that:
 * $(1): \quad \omega_1, \omega_2 \ne 0$
 * $(2): \quad \dfrac {\omega_1} {\omega_2} \notin \R$
 * $(3): \quad \forall z \in \C: \map f z = \map f {z + \omega_1} = \map f {z + \omega_2}$