\begin{definition}[Definition:Labeled Tree for Propositional Logic/Hypothesis Set]
Let $\left({T, \mathbf H, \Phi}\right)$ be a labeled tree for propositional logic.
The countable set $\mathbf H$ of WFFs of propositional logic is called the '''hypothesis set'''.
The elements of $\mathbf H$ are known as '''hypothesis WFFs'''.
The '''hypothesis set''' $\mathbf H$ is considered to be attached to the root node of $T$.
\end{definition}