\begin{definition}[Definition:Labeled Tree for Propositional Logic/Attached]
Let $\left({T, \mathbf H, \Phi}\right)$ be a labeled tree for propositional logic.
Let $t$ be a non-root node of $T$.
Let $\mathbf A$ be a WFF.
Then '''$\mathbf A$ is attached to $t$''' {{iff}} $\mathbf A = \Phi \left({t}\right)$.
All the WFFs in the hypothesis set $\mathbf H$ are considered to be '''attached to the root node'''.
\end{definition}