\begin{definition}[Definition:Fiber of Truth]
Let $P: X \to \set {\T, \F}$ be a propositional function defined on a domain $X$.
The '''fiber of truth (under $P$)''' is the preimage, or '''fiber''', of $\T$ under $P$:
:$\map {P^{-1} } \T := \set {x \in X: \map P x = \T}$
That is, the elements of $X$ whose image under $P$ is $\T$.
\end{definition}