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Let $\mathbf A$ be a WFF of propositional logic.

Let $\circ$ and $\ast$ be connectives.

Then $\circ$ is subordinate to $\ast$ (in $\mathbf A$) if and only if the scope of $\circ$ is a well-formed part of the scope of $\ast$.


Consider the WFF of propositional logic:

$\mathbf A := \paren {\paren {P_0 \land P_1} \implies \paren {\paren {P_2 \lor \neg P_3} \land \paren {P_4 \iff P_5} } }$

It is left as an exercise to the reader to demonstrate that $\mathbf A$ is well-formed.

The following statements are also left as exercises to prove:

$\mathbf B := \paren {\paren {P_2 \lor \neg P_3} \land \paren {P_4 \iff P_5} }$
is a well-formed part of $\mathbf A$.
  • The connective $\iff$ is subordinate to the occurrence of $\land$ in $\mathbf B$, but not to $\lor$ or $\neg$.