Fix concat natural transformation example

.gitignore

@@ -32,5 +32,6 @@
 *.synctex.gz
 *.toc
 *.vrb
+*.xdv
 *.xdy
 *.tdo

acknowledgements.tex

@@ -14,4 +14,15 @@ \chapter{Acknowledgements}
 Computation seminar 2013 attendees, and to my psychologist, María
 Paula Valderrama López.
 
+\section*{Errata}
+
+\begin{itemize}
+\item
+  February 15, 2019:
+  In example \ref{ex:natural-concat-haskell}, \texthaskell{concat} is a natural
+  transformation from the \texthaskell{[] . []} functor and into the
+  \texthaskell{[]} functor (instead of from and into the \texthaskell{[]}
+  functor). Thanks to Paulo Villela for reporting!
+\end{itemize}
+
 \clearemptydoublepage

naturals.tex

@@ -465,9 +465,9 @@ \section{Natural Transformations in Haskell}
   \label{ex:natural-concat-haskell}
 
   We can think of the \texthaskell{concat} function, which
-  concatenates a list of lists, as a natural transformation from and
-  into the \texthaskell{[]} functor. The type signature of this
-  function is:
+  concatenates a list of lists, as a natural transformation from the
+  \texthaskell{[] . []} functor and into the \texthaskell{[]} functor. The type
+  signature of this function is:
   \begin{codehaskell}
 concat :: [[a]] -> [a]
   \end{codehaskell}

preamble.tex

@@ -114,7 +114,7 @@
 %% Verbatim
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 
-\newfontfamily\dejavu{DejaVu Sans Mono}
+\newfontfamily\dejavu{DejaVuSansMono.ttf}
 
 \usepackage{fancyvrb}
 \usepackage{relsize}