Let $(X,\Sigma)$ be a measurable space, and let ${A_i}{i=1}^n$ be a sequence of disjoint measurable sets, and let ${a_i}{i=1}^n$ be a sequence of real numbers. A simple function is a function $f:X\to \mathbb R$ of the form \(f(x) = \sum_{k=1}^n a_k\chi_{A_k}(x)\) where $\chi_A$ is the characteristic function of $A$.
Wikidata ID: Q913022