.header.tex

\documentclass[a4paper]{article}    % base article class
\usepackage[utf8]{inputenc}         % allow utf8 input
\usepackage{graphicx}               % includegraphics
\usepackage{amsmath,amsthm}         % fancier math
%
%\usepackage{newtxtext}               % times new roman font
%\usepackage[bigdelims,cmintegrals,vvarbb]{newtxmath}
%
\usepackage[osf,sups]{Baskervaldx} % lining figures
\usepackage[bigdelims,cmintegrals,vvarbb,baskervaldx,frenchmath,upint]{newtxmath} % math font

%\usepackage[scale=.8]{inconsolata}                  % monospace font

\usepackage[T1]{fontenc}
\usepackage{cabin}
%\usepackage[zerostyle=d]{newtxtt}
%\renewcommand*\ffamilydefault{\ttdefault}

\usepackage[cal=boondoxo]{mathalfa} % mathcal from STIX, unslanted a bit
%
\usepackage{hyperref,url}           % hyperlinks and urls
%\usepackage{fancyvrb}               % fancier verbatim environment
\setlength{\parindent}{0pt}         % no paragraph indentation
\setlength{\parskip}{7pt}           % spacing between paragraphs
\setlength{\emergencystretch}{3em}  % prevent overfull lines
\pdfimageresolution 200             % change the default for included png files
\pdfinfoomitdate=1\pdftrailerid{}   % ensure reproducible PDF
\makeatletter\renewcommand{\verbatim@font}{\ttfamily\footnotesize}\makeatother
\newenvironment{gallery}{}{}
\newcommand{\galleryline}[1]{\includegraphics{#1}{\footnotesize\tt #1}\newline}
\theoremstyle{note}
\newtheorem{exercice}{Exercice}
\swapnumbers
\theoremstyle{plain}
\newtheorem{theorem}{Theorem}[section]
\newtheorem{lemma}[theorem]{Lemma}
\newtheorem{remark}[theorem]{Remark}
\newtheorem{definition}[theorem]{Definition}
\newtheorem{proposition}[theorem]{Proposition}
\setcounter{section}{-1}

\begin{document}