\usepackage{xcolor}
\usepackage{fontspec}
\usepackage[sc]{mathpazo}
\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}

\newcommand{\dn}{\stackrel{\mbox{\scriptsize def}}{=}}%
\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 ASCII text or PDFs. Every solution 
should be preceeded by the corresponding question. Solutions will only be accepted until 
30th December!}\bigskip}