diff --git a/latex/ystikz.sty b/latex/ystikz.sty
index 750d510..144fafc 100644
--- a/latex/ystikz.sty
+++ b/latex/ystikz.sty
@@ -69,7 +69,8 @@
       anchor=north
     }
   },
-  ssarbre/.style={isosceles triangle, draw, shape border rotate=90, minimum size=.7cm, child anchor=apex, anchor=apex}
+  ssarbre/.style={isosceles triangle, draw, shape border rotate=90, minimum size=.7cm, child anchor=apex, anchor=apex},
+  square/.style={regular polygon,regular polygon sides=4, inner sep=0pt, minimum size=.7cm}
 }
 
 \tikzstyle{basevertex} = [circle,