Simple Functions
Definition
A function {% f : \Omega \rightarrow E %} is called simple if the image {% f(\Omega) %} is a finite set.
That is, there is a set {% \{ c_1,c_2, ... ,c_n \} \subset E %} such that
{% f = \sum_{i=1}^n c_i I_i %}
where {% I_i %} is the indicator function for the set {% f^{-1}(c_i) %}
