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feat: annotate equations (#5)
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‎src/annotate-equations.sty‎

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% Annotate LaTeX Equations
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%
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% (c) 2022 by ST John, https://github.com/st--/
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% Licensed under MIT License
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%
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\NeedsTeXFormat{LaTeX2e}[1994/06/01]
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\ProvidesPackage{annotate-equations}
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[2022/03/29 v0.1.0 easily annotate equations using TikZ]
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%%% lualatex compatibility, from https://tex.stackexchange.com/a/351520/171664
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\RequirePackage{ifluatex}
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\ifluatex
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\RequirePackage{luatex85}
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\RequirePackage{pdftexcmds}
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\makeatletter
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\let\pdfstrcmp\pdf@strcmp
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\let\pdffilemoddate\pdf@filemoddate
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\makeatother
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\fi
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%%%
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\RequirePackage{tikz}
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\RequirePackage{xcolor}
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\usetikzlibrary{backgrounds}
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\usetikzlibrary{arrows,shapes}
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\usetikzlibrary{tikzmark} % for \tikzmarknode
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\usetikzlibrary{calc} % for computing the midpoint between two nodes, e.g. at ($(p1.north)!0.5!(p2.north)$)
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%%%%% SETTINGS %%%%%
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\newcommand{\eqnhighlightheight}{} % colorbox will shrink to content
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\renewcommand{\eqnhighlightheight}{\mathstrut} % colorbox will always have full height
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\newcommand{\eqnhighlightshade}{17} % light
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%\renewcommand{\eqnhighlightshade}{47} % dark
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\newcommand{\eqnannotationtext}[1]{\sffamily\footnotesize#1\strut} %%% TODO remove textsf/footnotesize/strut?
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\providecommand\EAmarkanchor{north} % default set to "above"
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\providecommand\EAwesteast{east} % default set to "right"
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\providecommand\EAlabelanchor{south} % default set to "label above"
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% for pgfkeys, see https://tex.stackexchange.com/a/34318/171664
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% for no-value keys, see https://tex.stackexchange.com/a/401848/171664
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\pgfkeys{
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/eqnannotate/.is family, /eqnannotate,
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above/.code = {\renewcommand\EAmarkanchor{north}},
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below/.code = {\renewcommand\EAmarkanchor{south}},
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left/.code = {\renewcommand\EAwesteast{west}},
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right/.code = {\renewcommand\EAwesteast{east}},
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label above/.code = {\renewcommand\EAlabelanchor{south}},
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label below/.code = {\renewcommand\EAlabelanchor{north}},
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}
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%%%%% %%%%%%%% %%%%%
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\newcommand*{\eqnhighlightcolorbox}[2]{%
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% \colorbox sets the second argument in text mode, so for use within equations we wrap it in $ $ again
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\mathchoice% to get right font size in each mode:
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{\colorbox{#1}{$\displaystyle #2$}}%
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{\colorbox{#1}{$\textstyle #2$}}%
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{\colorbox{#1}{$\scriptstyle #2$}}%
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{\colorbox{#1}{$\scriptscriptstyle #2$}}%
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}
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%%% the fbox with 0pt rule fixes the height of eqnmark vs eqnmarkbox issue
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\newcommand*{\eqnhighlightfbox}[2]{%
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% \fbox sets the second argument in text mode, so for use within equations we wrap it in $ $ again
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\mathchoice% to get right font size in each mode:
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{\begingroup\setlength{\fboxrule}{0pt}\fbox{$\displaystyle\color{#1}#2$}\endgroup}%
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{\begingroup\setlength{\fboxrule}{0pt}\fbox{$\textstyle\color{#1}#2$}\endgroup}%
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{\begingroup\setlength{\fboxrule}{0pt}\fbox{$\scriptstyle\color{#1}#2$}\endgroup}%
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{\begingroup\setlength{\fboxrule}{0pt}\fbox{$\scriptscriptstyle\color{#1}#2$}\endgroup}%
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}
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% . is the current color
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\newcommand*{\eqnhighlight}[2]{\begingroup\colorlet{currentcolor}{.}\eqnhighlightcolorbox{#1!\eqnhighlightshade}{\eqnhighlightheight #2}\endgroup}
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\newcommand*{\eqncolor}[2]{\begingroup\colorlet{currentcolor}{.}\eqnhighlightfbox{#1}{\eqnhighlightheight #2}\endgroup}
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%%% Arguments to \eqnmark[box]: [highlight color]{node name}{term to highlight}
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\newcommand*{\eqnmarkbox}[3][currentcolor]{\addvalue{#2}{#1}\tikzmarknode{#2}{\eqnhighlight{#1}{#3}}}
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\newcommand*{\eqnmark}[3][currentcolor]{\addvalue{#2}{#1}\tikzmarknode{#2}{\eqncolor{#1}{#3}}}
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% Store current color in a dictionary (lookup table),
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% from https://tex.stackexchange.com/a/48931/171664 :
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\def\addvalue#1#2{\expandafter\gdef\csname eqnannotate@data@#1\endcsname{#2}}
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\def\usevalue#1{%
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\ifcsname eqnannotate@data@#1\endcsname
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\csname eqnannotate@data@#1\expandafter\endcsname
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\else
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currentcolor%
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\fi
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}
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%%%%% Helpers for swapping north/south / west/east / -/+ depending on above/below / left/right etc.:
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\newcommand*{\swapNorthSouth}[1]{%
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\ifnum\pdfstrcmp{#1}{south}=0 north\else south\fi
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}
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\newcommand*{\swapWestEast}[1]{%
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\ifnum\pdfstrcmp{#1}{east}=0 west\else east\fi
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}
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\newcommand*{\EAxshift}[1]{%
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\ifnum\pdfstrcmp{#1}{east}=0 -0.3ex\else 0.3ex\fi
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}
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%%%%%
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\newcounter{eqnannotatenode}
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\newcommand*{\eqnannotateCurrentNode}{eqnannotatenode\theeqnannotatenode}
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\newcommand{\annotatetwo}[5][]{%
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\begingroup% %%% so we don't leak the \def's below
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\stepcounter{eqnannotatenode}%
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%%% #1: (optional) extra args for \node e.g. yshift=...
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\pgfkeys{/eqnannotate, #2}% %%% all configuration options
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\def\myEAmarkOne{#3}%
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\def\myEAmarkTwo{#4}%
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\colorlet{currentcolor}{.}
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\def\myEAtext{#5}%
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\def\myEAcolor{\usevalue{\myEAmarkOne}}%
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\begin{tikzpicture}[overlay,remember picture,>=stealth,nodes={align=left,inner ysep=1pt},<-]
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% default anchor is at center
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\node[anchor=\swapNorthSouth{\EAmarkanchor},color=\myEAcolor!85,#1] % color blended with white to 85%, any (optional) extra args #1
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(\eqnannotateCurrentNode) % use counter-based "local node"
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at ($(\myEAmarkOne.\EAmarkanchor)!0.5!(\myEAmarkTwo.\EAmarkanchor)$) % centered between the two nodes
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{\eqnannotationtext{\myEAtext}};
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% double arrow to two uses within the equation:
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\draw [<->,color=\myEAcolor] (\myEAmarkOne.\EAmarkanchor) |- ([yshift=0.1ex] \eqnannotateCurrentNode.\EAlabelanchor) -| (\myEAmarkTwo.\EAmarkanchor); % from node 1 via annotation to node 2, with anchor #6 each
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\end{tikzpicture}%
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\endgroup% %%% close group again
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}
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%%% \extractfirst from https://tex.stackexchange.com/a/115733/171664
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\RequirePackage{expl3}
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\RequirePackage{xparse}
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\ExplSyntaxOn
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\NewDocumentCommand{\extractfirst}{mm}
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{
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\tl_set:Nx #1 {\clist_item:Nn #2 { 1 } }
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}
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\ExplSyntaxOff
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%%%
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\newcommand{\annotate}[4][]{%
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\begingroup% %%% so we don't leak the \def's below
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\stepcounter{eqnannotatenode}%
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%
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%
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%
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% #1: (optional) extra args for \node e.g. yshift=...
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\pgfkeys{/eqnannotate, #2}
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\def\myEAmarks{#3}%
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\extractfirst\myEAmark\myEAmarks% %%% get first node for color and annotation
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\def\myEAtext{#4}%
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%
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%
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\colorlet{currentcolor}{.}
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\def\myEAcolor{\usevalue{\myEAmark}}%
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%
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%
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\def\myEAxshift{\EAxshift{\EAwesteast}}%
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\begin{tikzpicture}[overlay,remember picture,>=stealth,nodes={align=left,inner ysep=1pt},<-]
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\node[anchor=\swapNorthSouth{\EAmarkanchor} \swapWestEast{\EAwesteast},color=\myEAcolor!85,#1] % TODO for some reason, passing #1 through command doesn't work...
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% anchor=west: align left edge of text on top of tikzmark in equation
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% should be north west for below and south west for above ...
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(\eqnannotateCurrentNode) at (\myEAmark.\EAmarkanchor) % \EAmarkanchor north: above the equation, south: below
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{\eqnannotationtext{\myEAtext}};
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\foreach \EAmark in \myEAmarks
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\draw [color=\myEAcolor] (\EAmark.\EAmarkanchor) % arrow from the equation
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% \EAmarkanchor north: above the equation, south: below
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|- ([xshift=\myEAxshift,yshift=0.1ex] \eqnannotateCurrentNode.south \EAwesteast);
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% - south east: we want line to end at bottom right of annotation text;
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% - negative xshift makes it a little bit shorter;
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% - yshift for aesthetics (\strut is ever so slightly too tall).
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\end{tikzpicture}%
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\endgroup% %%% close group again
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}
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\endinput
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%%
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%% End of file

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