diff --git a/slides/cours_21.md b/slides/cours_21.md
index fa2120f124e8e4741b8d01326538c764a6dc54a1..3b711ea77aea8edff687352a9d21b79607b6d04d 100644
--- a/slides/cours_21.md
+++ b/slides/cours_21.md
@@ -373,8 +373,8 @@ int depth(node *qt) {
 noeud position(li, co, arbre)
     d = profondeur(arbre);
     tant_que (d >= 1)
-        index = 2 * ((li % 2^d) / 2^(d-1)) +
-            (col % 2^d) / 2^(d-1)
+        index = 2 * ((li % 2^d) / 2^(d-1))
+            + (col % 2^d) / 2^(d-1)
         arbre = arbre.enfant[index]
         d -= 1
     retourne arbre