added add_abbrevs(_i);
moved const_of_class/class_of_const to logic.ML;
added no_vars (from theory.ML);
added cert_def;
added const_expansion;
certify: refer to Consts.certify, which includes expansion;
%FIXME
%\chapter{Basic Concepts}\label{ch:basics}
%\section{The Isar proof language}
%%% Local Variables:
%%% mode: latex
%%% TeX-master: "isar-ref"
%%% End: