diff --git a/latex/yssymbols.tex b/latex/yssymbols.tex
index 64c7245..1fd216f 100644
--- a/latex/yssymbols.tex
+++ b/latex/yssymbols.tex
@@ -64,4 +64,5 @@
 \DeclareMathOperator*{\petito}{o}
 \DeclareMathOperator*{\grando}{O}
 
+\def\ssi{\@ifnextchar i{si et seulement s'}{si et seulement si\xspace}}
 \endinput
\ No newline at end of file