Primitive of Pointwise Sum of Functions/Proof 2

Proof
From Sum Rule for Derivatives:


 * $\ds \map {\dfrac \d {\d x} } {\sum_{i \mathop = 1}^n \map {f_i} x} = \sum_{i \mathop = 1}^n \map {\dfrac \d {\d x} } {\map {f_i} x}$

The result follows by definition of primitive.