diff --git a/mapytex/calculus/API/expression.py b/mapytex/calculus/API/expression.py
index 7fae25a..024d230 100644
--- a/mapytex/calculus/API/expression.py
+++ b/mapytex/calculus/API/expression.py
@@ -108,11 +108,13 @@ class Expression(object):
         >>> e = Expression.from_str("2x + 1 + 5x")
         >>> e
         <Exp: 2x + 1 + 5x>
+        >>> e = Expression.from_str("3")
+        >>> e
 
         """
         t = Tree.from_str(string)
         if typing:
-            return cls._post_precessing(t)
+            return cls._post_processing(t)
 
         return cls(t)
 
@@ -161,10 +163,10 @@ class Expression(object):
         if shuffle:
             raise NotImplemented("Can't suffle expression yet")
 
-        return cls._post_precessing(t)
+        return cls._post_processing(t)
 
     @classmethod
-    def _post_precessing(cls, t):
+    def _post_processing(cls, t):
         """ Post process the tree by typing it """
         tt = cls(t)._typing()
         try: