diff --git a/expression.py b/expression.py
index 737fd54..7c63309 100644
--- a/expression.py
+++ b/expression.py
@@ -1,4 +1,5 @@
 from Pile import Pile_chaine as Pile
+import math
 
 class Expression:
     "permet de représenter et manipuler une expression arithmpétique sous forme d'un arbre"
@@ -15,11 +16,18 @@ class Expression:
             return self.gauche.evalue() * self.droit.evalue()
         if self.racine == '+':
             return self.gauche.evalue() + self.droit.evalue()
+        if self.racine == '-':
+            return self.gauche.evalue() - self.droit.evalue()
+        if self.racine == '/':
+            return self.gauche.evalue() / self.droit.evalue()
+        
+    def racine_carre(self):
+        return math.sqrt(self.racine)
         
     def __str__(self):
         "affiche l'expression"
         exp = ""
-        if self.racine != '*' or self.racine != '+':
+        if self.racine != '*' or self.racine != '+' or self.racine != '-' or self.racine != '/':
             if self.gauche != None:
                 exp = "(" + exp + str(self.gauche)
             exp = exp + str(self.racine)
@@ -31,7 +39,7 @@ class Expression:
 def npi2tree(lst):
     p = Pile() 
     for elem in lst:
-        if elem == '+' or elem =='*':
+        if elem == '+' or elem =='*' or elem == '-' or elem == '/':
             racine = elem
             fils_d = p.depiler()
             fils_g = p.depiler()
@@ -45,10 +53,12 @@ def npi2tree(lst):
     
 if __name__ == "__main__":        
     exp = Expression('*',
-                     Expression('+',
-                                Expression(4, None, None),
+                     Expression('/',
+                                Expression(1.5, None, None),
                                 Expression(3, None, None)),
-                     Expression(6, None, None))
+                     Expression(6.5, None, None))
     print(exp.evalue())
     print(exp)
-    print(npi2tree(["6", "4", "3", "+", "*"]))
\ No newline at end of file
+    e = npi2tree(["6", "4", "3", "+", "-"])
+    print(e.evalue())
+