diff --git a/pymath/expression.py b/pymath/expression.py
index fb2809f..e48f460 100644
--- a/pymath/expression.py
+++ b/pymath/expression.py
@@ -324,7 +324,11 @@ class Expression(object):
         """
         return type(exp) == int or \
                 type(exp) == Fraction or \
+<<<<<<< HEAD
                 type(exp) == FormalExp
+=======
+                exp.isalpha()
+>>>>>>> Render ~work with letters still some bugs
 
     @staticmethod
     def isOperator(exp):
@@ -405,6 +409,15 @@ if __name__ == '__main__':
     #e = Expression(exp)
     #print(e)
 
+    exp="-2*a(12 + 1)(3-12)"
+    e = Expression(exp)
+    print(e)
+
+    # TODO: The next one doesn't work  |ven. janv. 17 14:56:58 CET 2014
+    #exp="-2*(-a)(12 + 1)(3-12)"
+    #e = Expression(exp)
+    #print(e)
+
     ## Can't handle it yet!!
     #exp="-(-2)"
     #test(exp)
diff --git a/pymath/render.py b/pymath/render.py
index 1b2dd6f..326224b 100644
--- a/pymath/render.py
+++ b/pymath/render.py
@@ -15,7 +15,7 @@ class Render(object):
 
     PRIORITY = {"^": 4,"*" : 3, "/": 3, ":": 3, "+": 2, "-":2, "(": 1}
 
-    def __init__(self, op_infix = {}, op_postfix = {}, other = {}, join = " ", type_render = {int: str, Fraction: str, FormalExp: str}):
+    def __init__(self, op_infix = {}, op_postfix = {}, other = {}, join = " ", type_render = {int: str, Fraction: str, str: str}):
         """Initiate the render
         
         @param op_infix: the dictionnary of infix operator with how they have to be render