moved recursion combinator to HOL/Library/Wfrec.thy -- it is so fundamental and well-known that it should survive recdef
\chapter{Presenting Theories}
\label{ch:thy-present}
By now the reader should have become sufficiently acquainted with elementary
theory development in Isabelle/HOL\@. The following interlude describes
how to present theories in a typographically
pleasing manner. Isabelle provides a rich infrastructure for concrete syntax
of the underlying $\lambda$-calculus language (see
{\S}\ref{sec:concrete-syntax}), as well as document preparation of theory texts
based on existing PDF-{\LaTeX} technology (see
{\S}\ref{sec:document-preparation}).
As pointed out by Leibniz\index{Leibniz, Gottfried Wilhelm} more than 300
years ago, \emph{notions} are in principle more important than
\emph{notations}, but suggestive textual representation of ideas is vital to
reduce the mental effort to comprehend and apply them.
\input{Documents/document/Documents.tex}
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