Scaling limits of discrete holomorphic functions

One of the most natural and challenging issues in discrete complex analysis is to prove the convergence of discrete holomorphic functions to their continuous counterparts. This article is to solve the open problem in the general setting. To this end we introduce new concepts of discrete surface measure and discrete outer normal vector and establish the discrete Cauchy-Pompeiu integral formula, \begin{eqnarray*} f(\zeta)=\displaystyle{\int_{\partial B^h}} \mathcal{K}^h(z,\zeta) f(z)dS^h(z)+\displaystyle{\int_{B^h}} E^h(\zeta-z) \partial_{\bar z}^h f (z)dV^h(z),\end{eqnarray*} which results in the uniform convergence of the scaling limits of discrete holomorphic functions up to second order derivatives in the standard square lattices.