.Rproj.user/441ADA46/sources/s-FE609B0F/A4381D75-contents

\documentclass{report}
\usepackage[most]{tcolorbox}
\usepackage{lmodern}
\usepackage{lipsum}
\usepackage[explicit]{titlesec}
\usepackage{varwidth}

\tcbset{
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        attach boxed title to top left={%
            yshift*=-\tcboxedtitleheight/2,
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        boxed title style={colframe=gray}
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}

\newtcbtheorem[auto counter]{mylemma}{Lemma}{%
    orange
    }{lm}

\titleformat{\chapter}[display]
  {\normalfont\Large\bfseries}
  {}
  {}
  {%
    \begin{tcolorbox}[orange, halign=center, valign=center, title=test, overlay={\node[draw=gray, fill=orange!40, rounded corners, anchor=east, font=\small\bfseries] at ([xshift=-5mm]frame.south east){2016-2017};}]%, title=Title]
    #1
   \end{tcolorbox}%
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\titleformat{\section}
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\titlespacing*{\section}
  {0pt}{4.5ex plus 1ex minus .2ex}{1ex plus .2ex}

\begin{document}

\chapter*{Diagonalizar matrices}
\section{Test numbered section}
\begin{mylemma}{Test}{a}
\lipsum[3]
\end{mylemma}

\begin{mylemma}{Test}{a}
\lipsum[3]
\end{mylemma}

\section*{Test unnumbered section}
\lipsum[4]
%\section{Test numbered section with a long title; in fact, it spans two lines}
%\lipsum[4]

\end{document}