At the end of Chapter 1 we introduced the holomorphic functions, that is, those functions f ∈ C1(Ω) that satisfy the Cauchy-Riemann differential equation \(\frac{{\partial f}}{{\partial \bar z}} = 0\) throughout an open set Ω ⊆ ℂ. As an immediate consequence of the topological tools developed in that chapter we found that the holomorphic functions enjoyed the following remarkable property (Cauchy’s theorem 1.1 1.4).