\usepackage{xcolor}
\usepackage{fontspec}
\usepackage[sc]{mathpazo}
\setmainfont[Ligatures=TeX]{Palatino Linotype}
\usepackage{amssymb}
\usepackage{amsmath}
\usepackage{menukeys}
\@ifpackageloaded{hyperref}{}{\usepackage{hyperref}}

\definecolor{darkblue}{rgb}{0,0,0.6}
\hypersetup{colorlinks=true}
\hypersetup{linkcolor=darkblue}
\hypersetup{urlcolor=darkblue}


\ifx\foobar\undefined \else
  \newcommand{\dn}{\stackrel{\mbox{\scriptsize def}}{=}}%
\fi

\definecolor{codegray}{gray}{0.9}

\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	

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


\newcommand{\HEADER}{{\bf Please submit your solutions to the
email address 7ccsmsen at gmail dot com. Please submit only one
homework per email. Please also submit only
ASCII text or PDFs. Every solution should be preceded by the
corresponding question, 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
30th December!}\bigskip}