Add introduction to the third chapter

setup.org

@@ -162,9 +162,9 @@ See more information [[https://tex.stackexchange.com/questions/68516/avoid-that-
     style=numeric-comp, % bib style
     hyperref=true,  % activate hyperref support
     backref=true,   % activate backrefs
-    isbn=false,     % don't show isbn tags
+    isbn=true,      % don't show isbn tags
     url=false,      % don't show url tags
-    doi=false,      % don't show doi tags
+    doi=true,       % don't show doi tags
     urldate=long,   % display type for dates
     maxnames=3,     %
     minnames=1,     %
@@ -187,17 +187,15 @@ See more information [[https://tex.stackexchange.com/questions/68516/avoid-that-
   {\item}
 #+end_src
 
-Remove ISSN, DOI and URL to shorten the bibliography.
+Remove ISBN if DOI is available.
 #+begin_src latex
-\AtEveryBibitem{%
-  \clearfield{urlyear}
-  \clearfield{urlmonth}
-  \clearfield{note}
- \clearfield{issn} % Remove issn
- \clearfield{doi} % Remove doi
-\ifentrytype{online}{}{% Remove url except for @online
-  \clearfield{url}
-}
+\DeclareSourcemap{
+  \maps[datatype=bibtex]{
+     \map{
+        \step[fieldsource=doi,final]
+        \step[fieldset=isbn,null]
+        }
+      }
 }
 #+end_src
 
@@ -301,6 +299,23 @@ And then use quotes as:
 
 Note that org-ref links won't work here because the attr latex will be pasted as-is in the .tex file.
 
+** Footnotes
+#+begin_src latex
+\usepackage[perpage]{footmisc}
+#+end_src
+
+** Automatic non-breaking space for citations
+#+begin_src latex
+\let\myRef\ref
+\renewcommand\ref{\unskip~\myRef}
+
+\let\myEqref\eqref
+\renewcommand\eqref{\unskip~\myEqref}
+
+\let\myCite\cite
+\renewcommand\cite{\unskip~\myCite}
+#+end_src
+
 ** Setspace for controlling line spacing
 #+begin_src latex
 \usepackage{setspace}