\[\newcommand{\vect}[1]{\vec{\boldsymbol{#1}}}
\newcommand{\uvect}[1]{\hat{\boldsymbol{#1}}}
\newcommand{\abs}[1]{\lvert#1\rvert}
\newcommand{\norm}[1]{\lVert#1\rVert}
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\newcommand{\ddiff}[3][]{\frac{\delta^{#1} #2}{\delta{#3}^{#1}}}
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% These replace SIunitx. They should not be defined in LaTeX.
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\]
