Rename section on semantic

spec/doc.tex

@@ -722,8 +722,7 @@ have an arbitrary order after instantiation.
 Nevertheless, consumers of Alethe must consider the possible
 implicit reordering of equalities.
 
-% PF TODO why concrete?  Why not simply call it Semantics?
-\section{The Concrete Semantics}
+\section{The Semantics of Alethe}
 \label{sec:semantic}
 
 Most of the content is taken from the presentation and the correctness proof of