doc-src/Logics/abstract.txt

Updated datatype documentation with a few hints

Isabelle's Object-Logics.  Report 286.

This is the third of the Isabelle manuals.  It covers Isabelle's built-in
object logics: first-order logic (FOL), Zermelo-Fraenkel set theory (ZF),
higher-order logic (HOL), the classical sequent calculus (LK), and
constructive type theory (CTT).  The final chapter discusses how to define
new logics.  This manual assumes familiarity with Report 280, Introduction
to Isabelle.