diff --git a/packages/macros.sty b/packages/macros.sty
index f1d52d2..ca88f6a 100644
--- a/packages/macros.sty
+++ b/packages/macros.sty
@@ -2,6 +2,8 @@
 
 \RequirePackage{amsfonts}                                % Include missing symbols s.a "Natural Numbers"
 
+\usepackage{amsthm}   % for 'proof' environment
+
 % Snippet to add dots to TOC
 % Thanks to "user11232" at https://tex.stackexchange.com/questions/53898/how-to-get-lines-with-dots-in-the-table-of-contents-for-sections
 %\usepackage{tocloft}
@@ -42,6 +44,7 @@
 \newcommand{\functiondef}[2]{\hspace{15pt}#1 \longmapsto #2}
 \newcommand{\otherwise}{\text{Sinon}}
 %\newcommand{\otherwise}{\text{Otherwise}}
+\DeclareMathOperator{\union}{\cup}
 
 \renewcommand{\smallskip}{\vspace{3pt}}
 \renewcommand{\medskip}{\vspace{6pt}}