Let $f : X \to X$ be a D2660: Set endomorphism such that

(i)	$E \subseteq X$ is a D78: Subset of $X$
(ii)	$I_E : X \to \{ 0, 1 \}$ is the D41: Indicator function of $E$ within $X$

Then \begin{equation} I_E \circ f = I_{f^{-1}(E)} \end{equation}