Curly Brace Error

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% Lecture Specific Information to Fill Out
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\newcommand{\LectureTitle}{Notas de Aula \#2}
%\newcommand{\LectureDate}{\today}
\newcommand{\LectureDate}{30\ de Novembro,\ 2013}
\newcommand{\LectureClassName}{MAT\ D04}
\newcommand{\LatexerName}{Carlos\ V.A.\ Silva}
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% Change "article" to "report" to get rid of page number on title page
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\usepackage{afterpage}
\usepackage{abstract}
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\usepackage{chemfig} % for drawing chemical compounds
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%        \tikzstyle{underbrace text style}=[font=\tiny, below, pos=.5, yshift=-3mm]
%emoticons
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%Code Listing
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%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Some tools
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        \draw (block-1-2.south) node[below=0.1cm] {$\longleftarrow$};
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        \draw (block-1-7.north) node[above=0.1cm,scale=0.7] {6};
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