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%% The LaTeX Companion, 3ed
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%% Example 9-4-1 on page I-678 in "Predefined alphabet identifiers".
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%% Copyright (C) 2022 Frank Mittelbach
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%% of the LaTeX Project Public License, either version 1.3c
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%% See https://www.latex-project.org/lppl.txt for details.
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\documentclass{tlc3exa}
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\begin{document}
Therefore, $\mathsf{G}$ can be computed as
\begin{equation}
  \mathsf{G} = \mathcal{A} +
               \sum_{i=1}^{n} \mathcal{B}_{i}
\end{equation}
\end{document}