deletions | additions       diff --git a/header.tex b/header.tex  index 7a9fbe6..cb6479f 100644  --- a/header.tex  +++ b/header.tex 
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\newcommand{\mat}[4] {\begin{bmatrix} #1 & #2 \\ #3 & #4 \end{bmatrix}} \newcommand{\vec}[2] {\begin{bmatrix} #1 \\ #2 \end{bmatrix}}