ThmDex – An index of mathematical definitions, results, and conjectures.
Formulation 0
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}