diff --git a/aprendizations/learnapp.py b/aprendizations/learnapp.py
index 03490ee..ed57c84 100644
--- a/aprendizations/learnapp.py
+++ b/aprendizations/learnapp.py
@@ -370,7 +370,6 @@ class LearnApp(object):
 
             t['path'] = path.join(g.graph['prefix'], tref)    # prefix/topic
 
-
     # ========================================================================
     # methods that do not change state (pure functions)
     # ========================================================================
@@ -379,6 +378,7 @@ class LearnApp(object):
     # Buils dictionary of question factories
     # ------------------------------------------------------------------------
     def make_factory(self) -> Dict[str, QFactory]:
+
         logger.info('Building questions factory:')
         factory: Dict[str, QFactory] = {}
         g = self.deps
diff --git a/aprendizations/questions.py b/aprendizations/questions.py
index cb15512..d66c2c6 100644
--- a/aprendizations/questions.py
+++ b/aprendizations/questions.py
@@ -234,7 +234,8 @@ class QuestionText(Question):
 
         self.set_defaults(QDict({
             'text': '',
-            'correct': [],
+            'correct': [],  # no correct answers, always wrong
+            'transform': [],  # transformations applied to the answer, in order
             }))
 
         # make sure its always a list of possible correct answers
@@ -244,12 +245,36 @@ class QuestionText(Question):
         # make sure all elements of the list are strings
         self['correct'] = [str(a) for a in self['correct']]
 
+        # make sure that the answers are invariant with respect to the filters
+        if any(c != self.transform(c) for c in self['correct']):
+            logger.warning(f'in "{self["ref"]}", correct answers are not '
+                           'invariant wrt transformations')
+
+    # ------------------------------------------------------------------------
+    # apply optional filters to the answer
+    def transform(self, ans):
+        for f in self['transform']:
+            if f == 'remove_space':
+                ans = ans.replace(' ', '')
+            elif f == 'trim':
+                ans = ans.strip()
+            elif f == 'normalize_space':
+                ans = re.sub(r'\s+', ' ', ans.strip())
+            elif f == 'lower':
+                ans = ans.lower()
+            elif f == 'upper':
+                ans = ans.upper()
+            else:
+                logger.warning(f'in "{self["ref"]}", unknown transform "{f}"')
+        return ans
+
     # ------------------------------------------------------------------------
     def correct(self) -> None:
         super().correct()
 
         if self['answer'] is not None:
-            self['grade'] = 1.0 if self['answer'] in self['correct'] else 0.0
+            answer = self.transform(self['answer'])  # apply transformations
+            self['grade'] = 1.0 if answer in self['correct'] else 0.0
 
 
 # ============================================================================
diff --git a/aprendizations/student.py b/aprendizations/student.py
index 10fad38..6319bb2 100644
--- a/aprendizations/student.py
+++ b/aprendizations/student.py
@@ -3,7 +3,7 @@
 from datetime import datetime
 import logging
 import random
-from typing import Dict, List, Optional, Tuple
+from typing import List, Optional, Tuple
 
 # third party libraries
 import networkx as nx
@@ -176,7 +176,7 @@ class StudentState(object):
             dt = now - s['date']
             try:
                 forgetting_factor = self.deps.nodes[tref]['forgetting_factor']
-                s['level'] *= forgetting_factor ** dt.days   # forgetting factor
+                s['level'] *= forgetting_factor ** dt.days  # forgetting factor
             except KeyError:
                 logger.warning(f'Topic {tref} is not on the graph!')
 
--
libgit2 0.21.2