docs: improve structure

docs/logic.tex

@@ -74,8 +74,6 @@ Furthermore, $\SigAx$ is a set of \emph{axioms}, that is, terms $\term$ of type
 Again, the grammar of terms and their typing rules are defined below, and depends only on $\SigType$ and $\SigFn$, not on $\SigAx$.
 Elements of $\SigAx$ are ranged over by $\sigax$.
 
-\section{Syntax}
-
 \subsection{Grammar}\label{sec:grammar}
 
 \paragraph{Syntax.}
@@ -276,7 +274,7 @@ In writing $\vctx, x:\type$, we presuppose that $x$ is not already declared in $
 	}
 \end{mathparpagebreakable}
 
-\subsection{Timeless Propositions}
+\subsection{Timeless propositions}
 
 Some propositions are \emph{timeless}, which intuitively means that step-indexing does not affect them.
 This is a \emph{meta-level} assertions about propositions, defined by the following judgment.
@@ -285,7 +283,7 @@ This is a \emph{meta-level} assertions about propositions, defined by the follow
 
 \ralf{Define a judgment that defines them.}
 
-\subsection{Base logic}
+\subsection{Proof rules}
 
 \ralf{Go on checking below.}
 The judgment $\vctx \mid \pfctx \proves \prop$ says that with free variables $\vctx$, proposition $\prop$ holds whenever all assumptions $\pfctx$ hold.