In this course, we have looked at three different but related logics. In Propositional Logic, we focussed on logical operators. In Relational Logic, we extended our language to include variables and quantifiers. In Functional Logic, we added functional terms.
Each of these logics is effectively an extension of its predecessor. The languages are increasingly expressive. The semantics of each builds upon the semantics of its predecessors. And the proof methods of each extend the proof methods accordingly. In fact, we can think of all three of these logics as parts of a single overarching logic that includes the details of all of them, viz. Herbrand Logic.
We begin this final chapter with a review the main concepts of Herbrand Logic. There is nothing new here, just a reminder of the essential details, compressed here into a few pages  to emphasize the important ideas in the course and to make clear how they are related to each other. With that behind us, we look at some extensions to Herbrand Logic, indicating areas for further study and research.
