diff --git a/expression.py b/expression.py
index 428cbfc..861fb4b 100644
--- a/expression.py
+++ b/expression.py
@@ -132,6 +132,12 @@ class Expression(object):
                 else:
                     tokens.append(int(character))
 
+            elif character.isalpha():
+                if str(tokens[-1]).isalpha():
+                    tokens[-1] += character
+                else:
+                    tokens.append(character)
+
             elif character in "+-*/)":
                 tokens.append(character)
 
@@ -143,7 +149,6 @@ class Expression(object):
             elif character != " ":
                 raise ValueError("{} is an unvalid character".format(character))
 
-        print(tokens[1:])
         return tokens[1:]
 
     # ---------------------
@@ -292,7 +297,9 @@ class Expression(object):
         :returns: True if the expression can be a number and false otherwise
 
         """
-        return type(exp) == int or type(exp) == Fraction
+        return type(exp) == int or \
+                type(exp) == Fraction or \
+                exp.isalpha()
 
     @staticmethod
     def isOperator(exp):
@@ -360,6 +367,15 @@ if __name__ == '__main__':
     exp="-2*4(12 + 1)(3-12)"
     test(exp)
 
+    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/render.py b/render.py
index 05def52..191ca05 100644
--- a/render.py
+++ b/render.py
@@ -16,7 +16,7 @@ class Render(object):
 
     PRIORITY = {"*" : 3, "/": 3, "+": 2, "-":2, "(": 1}
 
-    def __init__(self, op_infix = {}, op_postfix = {}, other = {}, join = " ", type_render = {int: str, Fraction: 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
@@ -107,7 +107,9 @@ class Render(object):
         :param posi: "after"(default) if the operande will be after the operator, "before" othewise
         :returns: bollean
         """
-        if self.isNumber(operande) and operande < 0:
+        if self.isNumber(operande) \
+                and type(operande) != str \
+                and operande < 0:
             return 1
         elif not self.isNumber(operande):
             # Si c'est une grande expression ou un chiffre négatif
@@ -159,7 +161,10 @@ class Render(object):
         :returns: True if the expression can be a number and false otherwise
 
         """
-        return type(exp) == int or type(exp) == Fraction
+        return type(exp) == int or \
+                type(exp) == Fraction or \
+                (type(exp) == str and exp.isalpha())
+        #return type(exp) == int or type(exp) == Fraction
 
     def isOperator(self, exp):
         """Check if the expression is in self.operators
@@ -209,7 +214,7 @@ def texFrac(frac):
 tex_infix = {"+": " + ", "-": " - ", "*": " \\times "}
 tex_postfix = {"/": texSlash}
 tex_other = {"(": "(", ")": ")"}
-tex_type_render = {int: str, Fraction: texFrac}
+tex_type_render = {int: str, Fraction: texFrac, str: str}
 
 tex_render = Render(tex_infix, tex_postfix, tex_other, type_render = tex_type_render)