diff --git a/latex/yssymbols.sty b/latex/yssymbols.sty
index b2f1dd0..33d95c6 100644
--- a/latex/yssymbols.sty
+++ b/latex/yssymbols.sty
@@ -17,6 +17,7 @@
 \def\Z{\mathbb{Z}}
 \def\C{\mathbb{C}}
 \def\diff{\mathrm d}
+\def\e{\mathrm e}
 \def\enstq#1#2{\left\{ #1 \ \middle|\ #2\right\}}
 \def\prive{\setminus}
 \let\vec\overrightarrow