Fix typo in Section 12.2 of the Open Logic Text

Author: FnControlOption

content/first-order-logic/axiomatic-deduction/axioms-rules-propositional.tex

@@ -10,7 +10,7 @@
       {\olfileid{fol}{axd}{prp}}
       {\olfileid{pl}{axd}{prp}}
 
-\olsection{Axiom and Rules for the Propositional Connectives}
+\olsection{Axioms and Rules for the Propositional Connectives}
 
 \begin{defn}[Axioms]
 The set of $\PAx$ of \emph{axioms} for the propositional connectives comprises