Does calculus for complex numbers exists? did any one ever tried to make research on this?
What would it mean to have complex numbers calculus? for instance: What is the meaning of $$\lim_{x\to z} f(x) = L \\ for \ complex \ values \ z, L, \ and \ the \ complex \ variable \ (x)$$
What is the meaning of $$\frac {dy}{dx}=\sqrt {-1}$$
Or what's the meaning of $$\int_{z_2}^{z_1} F(z) dz = \sqrt {-1},\ for \ complex \ values \ z, z_1, z_2$$