\usepackage{xcolor}
%%\usepackage{fontspec}
\usepackage[sc]{mathpazo}
\usepackage{fontspec}
\setmainfont[Ligatures=TeX]{Palatino Linotype}
\usepackage{amssymb}
\usepackage{amsmath}
\usepackage{menukeys}
\definecolor{darkblue}{rgb}{0,0,0.6}
\usepackage[colorlinks=true,urlcolor=darkblue,linkcolor=darkblue]{hyperref}
\usepackage{soul}

%%% for regular expressions and values
\newcommand{\ZERO}{\mbox{\bf 0}}
\newcommand{\ONE}{\mbox{\bf 1}}
\newcommand{\Left}{\textit{Left}}
\newcommand{\Right}{\textit{Right}}
\newcommand{\Der}{\textit{Der}}
\newcommand{\der}{\textit{der}}
\newcommand{\Ders}{\textit{Ders}}
\newcommand{\ders}{\textit{ders}}
\newcommand{\inj}{\textit{inj}}
\newcommand{\nullable}{\textit{nullable}}

%%% for trees
%% http://anorien.csc.warwick.ac.uk/mirrors/CTAN/graphics/pgf/contrib/forest/forest.pdf

\newcommand\grid[1]{%
\begin{tikzpicture}[baseline=(char.base)]
  \path[use as bounding box]
    (0,0) rectangle (1em,1em);
  \draw[red!50, fill=red!20]
    (0,0) rectangle (1em,1em);
  \node[inner sep=1pt,anchor=base west]
    (char) at (0em,\gridraiseamount) {#1};
\end{tikzpicture}}
\newcommand\gridraiseamount{0.12em}

\makeatletter
\newcommand\Grid[1]{%
  \@tfor\z:=#1\do{\grid{\z}}}
\makeatother	

\newcommand\Vspace[1][.3em]{%
  \mbox{\kern.06em\vrule height.3ex}%
  \vbox{\hrule width#1}%
  \hbox{\vrule height.3ex}}

\def\VS{\Vspace[0.6em]}


\newcommand{\dn}{\stackrel{\mbox{\scriptsize def}}{=}}
\newcommand{\defn}[1]{\textit{\textbf{#1}}}
\newcommand{\dq}[1]{\mbox{\tt{"}}#1\mbox{\tt{"}}}

\definecolor{codegray}{gray}{0.9}

\makeatletter
\def\fnote{\gdef\@thefnmark{}\@footnotetext}
\makeatother

\newcommand{\HEADER}{{\bf Please submit your solutions via email. Please submit 
only ASCII text or PDFs. Every solution should be preceeded by the corresponding 
question text, like:

\begin{center}
\begin{tabular}{ll}
Q$n$: & \ldots a difficult question from me\ldots\\
A:    & \ldots an answer from you \ldots\\
Q$n+1$ & \ldots another difficult question\ldots\\
A:     & \ldots another brilliant answer from you\ldots
\end{tabular}
\end{center}

\noindent Solutions will only be accepted until 20th December! Please send only
one homework per email.}\bigskip}

\newcommand{\POSTSCRIPT}{
{\bf (Optional)} This question is for you to provide 
regular feedback to me: for example
what were the most interesting, least interesting, or confusing 
parts in this lecture? Any problems with my Scala code? Please 
feel free to share any other questions or concerns. Also, all my
material is \st{crap} imperfect. If you have any suggestions for
improvement, I am very grateful to hear.}