Let $X$ be a D11: Set such that

(i)	$E \subseteq X$ is a D78: Subset of $X$
(ii)	$X \setminus E$ is the D79: Set complement of $E$ within $X$
(iii)	$I_{X \setminus E} : X \to \{ 0, 1 \}$ is an D41: Indicator function on $X$ with respect to $X \setminus E$

Then \begin{equation} I_{X \setminus E} = 1 - I_E \end{equation}