deletions | additions       diff --git a/untitled.tex b/untitled.tex  index f4a90ee..79ba8e9 100644  --- a/untitled.tex  +++ b/untitled.tex 
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\usepackage{amsmath}  \section{The original model}  The equations in the original model are as follows: 
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a & b \\  c & d   \end{matrix}