diff --git a/common/lib/capa/capa_problem.py b/common/lib/capa/capa_problem.py
index 93d5620aae..b14001ef03 100644
--- a/common/lib/capa/capa_problem.py
+++ b/common/lib/capa/capa_problem.py
@@ -12,6 +12,8 @@ Main module which shows problems (of "capa" type).
 This is used by capa_module.
 '''
 
+from __future__ import division
+
 import copy
 import logging
 import math
@@ -32,20 +34,10 @@ import inputtypes
 from util import contextualize_text
 
 # to be replaced with auto-registering
-from responsetypes import NumericalResponse, FormulaResponse, CustomResponse, SchematicResponse, MultipleChoiceResponse, TrueFalseResponse, ExternalResponse, ImageResponse, OptionResponse, SymbolicResponse
+import responsetypes
 
 # dict of tagname, Response Class -- this should come from auto-registering
-response_types = {'numericalresponse': NumericalResponse,
-                  'formularesponse': FormulaResponse,
-                  'customresponse': CustomResponse,
-                  'schematicresponse': SchematicResponse,
-                  'externalresponse': ExternalResponse,
-                  'multiplechoiceresponse': MultipleChoiceResponse,
-                  'truefalseresponse': TrueFalseResponse,
-                  'imageresponse': ImageResponse,
-                  'optionresponse': OptionResponse,
-                  'symbolicresponse': SymbolicResponse,
-                  }
+response_tag_dict = dict([(x.response_tag,x) for x in responsetypes.__all__])
 
 entry_types = ['textline', 'schematic', 'choicegroup', 'textbox', 'imageinput', 'optioninput']
 solution_types = ['solution']    			# extra things displayed after "show answers" is pressed
@@ -65,7 +57,7 @@ global_context = {'random': random,
                   'eia': eia}
 
 # These should be removed from HTML output, including all subelements
-html_problem_semantics = ["responseparam", "answer", "script"]
+html_problem_semantics = ["responseparam", "answer", "script","hintgroup"]
 
 #log = logging.getLogger(__name__)
 log = logging.getLogger('mitx.common.lib.capa.capa_problem')
@@ -209,7 +201,7 @@ class LoncapaProblem(object):
         oldcmap = self.correct_map				# old CorrectMap
         newcmap = CorrectMap()					# start new with empty CorrectMap
         for responder in self.responders.values():
-            results = responder.get_score(answers,oldcmap)      # call the responsetype instance to do the actual grading
+            results = responder.evaluate_answers(answers,oldcmap)      # call the responsetype instance to do the actual grading
             newcmap.update(results)
         self.correct_map = newcmap
         log.debug('%s: in grade_answers, answers=%s, cmap=%s' % (self,answers,newcmap))
@@ -248,7 +240,8 @@ class LoncapaProblem(object):
         '''
         return contextualize_text(etree.tostring(self.extract_html(self.tree)), self.context)
 
-    # ======= Private ========
+    # ======= Private Methods Below ========
+
     def extract_context(self, tree, seed=struct.unpack('i', os.urandom(4))[0]):  # private
         '''
         Extract content of <script>...</script> from the problem.xml file, and exec it in the
@@ -296,15 +289,17 @@ class LoncapaProblem(object):
         problemid = problemtree.get('id')    # my ID
 
         if problemtree.tag in inputtypes.get_input_xml_tags():
-            # status is currently the answer for the problem ID for the input element,
-            # but it will turn into a dict containing both the answer and any associated message
-            # for the problem ID for the input element.
+
             status = "unsubmitted"
             msg = ''
+            hint = ''
+            hintmode = None
             if problemid in self.correct_map:
                 pid = problemtree.get('id')
                 status = self.correct_map.get_correctness(pid)
                 msg = self.correct_map.get_msg(pid)
+                hint = self.correct_map.get_hint(pid)
+                hintmode = self.correct_map.get_hintmode(pid)
 
             value = ""
             if self.student_answers and problemid in self.student_answers:
@@ -316,7 +311,10 @@ class LoncapaProblem(object):
                                                    state={'value': value,
                                                           'status': status,
                                                           'id': problemtree.get('id'),
-                                                          'feedback': {'message': msg}
+                                                          'feedback': {'message': msg,
+                                                                       'hint' : hint,
+                                                                       'hintmode' : hintmode,
+                                                                       }
                                                           },
                                                    use='capa_input')
             return render_object.get_html()  # function(problemtree, value, status, msg) # render the special response (textline, schematic,...)
@@ -352,7 +350,7 @@ class LoncapaProblem(object):
         '''
         response_id = 1
 	self.responders = {}
-        for response in tree.xpath('//' + "|//".join(response_types)):
+        for response in tree.xpath('//' + "|//".join(response_tag_dict)):
             response_id_str = self.problem_id + "_" + str(response_id)
             response.set('id',response_id_str)				# create and save ID for this response
             response_id += 1
@@ -366,7 +364,7 @@ class LoncapaProblem(object):
                 entry.attrib['id'] = "%s_%i_%i" % (self.problem_id, response_id, answer_id)
                 answer_id = answer_id + 1
 
-            responder = response_types[response.tag](response, inputfields, self.context, self.system)	# instantiate capa Response
+            responder = response_tag_dict[response.tag](response, inputfields, self.context, self.system) # instantiate capa Response
 	    self.responders[response] = responder				# save in list in self
 
         # <solution>...</solution> may not be associated with any specific response; give IDs for those separately
diff --git a/common/lib/capa/correctmap.py b/common/lib/capa/correctmap.py
index 3eac98cc3a..f694391cc6 100644
--- a/common/lib/capa/correctmap.py
+++ b/common/lib/capa/correctmap.py
@@ -5,7 +5,16 @@
 
 class CorrectMap(object):
     '''
-    Stores (correctness, npoints, msg) for each answer_id.
+    Stores map between answer_id and response evaluation result for each question
+    in a capa problem.  The response evaluation result for each answer_id includes
+    (correctness, npoints, msg, hint, hintmode).
+
+    - correctness : either 'correct' or 'incorrect'
+    - npoints     : None, or integer specifying number of points awarded for this answer_id
+    - msg         : string (may have HTML) giving extra message response (displayed below textline or textbox)
+    - hint        : string (may have HTML) giving optional hint (displayed below textline or textbox, above msg)
+    - hintmode    : one of (None,'on_request','always') criteria for displaying hint
+
     Behaves as a dict.
     '''
     cmap = {}
@@ -13,11 +22,14 @@ class CorrectMap(object):
     def __init__(self,*args,**kwargs):
         self.set(*args,**kwargs)
 
-    def set(self,answer_id=None,correctness=None,npoints=None,msg=''):
+    def set(self, answer_id=None, correctness=None, npoints=None, msg='', hint='', hintmode=None):
         if answer_id is not None:
             self.cmap[answer_id] = {'correctness': correctness,
                                     'npoints': npoints,
-                                    'msg': msg }
+                                    'msg': msg,
+                                    'hint' : hint,
+                                    'hintmode' : hintmode,
+                                    }
 
     def __repr__(self):
         return repr(self.cmap)
@@ -64,6 +76,20 @@ class CorrectMap(object):
     def get_msg(self,answer_id):
         return self.get_property(answer_id,'msg','')
 
+    def get_hint(self,answer_id):
+        return self.get_property(answer_id,'hint','')
+
+    def get_hintmode(self,answer_id):
+        return self.get_property(answer_id,'hintmode',None)
+
+    def set_hint_and_mode(self,answer_id,hint,hintmode):
+        '''
+          - hint     : (string) HTML text for hint
+          - hintmode : (string) mode for hint display ('always' or 'on_request')
+        '''
+        self.set_property(answer_id,'hint',hint)
+        self.set_property(answer_id,'hintmode',hintmode)
+
     def update(self,other_cmap):
         '''
         Update this CorrectMap with the contents of another CorrectMap
diff --git a/common/lib/capa/inputtypes.py b/common/lib/capa/inputtypes.py
index 10fbdb7f98..1fa51f2f84 100644
--- a/common/lib/capa/inputtypes.py
+++ b/common/lib/capa/inputtypes.py
@@ -32,44 +32,57 @@ def get_input_xml_tags():
     return SimpleInput.get_xml_tags()
 
 class SimpleInput():# XModule
-    ''' Type for simple inputs -- plain HTML with a form element
-
-    State is a dictionary with optional keys: 
-    * Value
-    * ID
-    * Status (answered, unanswered, unsubmitted)
-    * Feedback (dictionary containing keys for hints, errors, or other 
-      feedback from previous attempt)
-
+    '''
+    Type for simple inputs -- plain HTML with a form element
     '''
 
     xml_tags = {} ## Maps tags to functions
 
     def __init__(self, system, xml, item_id = None, track_url=None, state=None, use = 'capa_input'):
+        '''
+        Instantiate a SimpleInput class.  Arguments:
+
+        - system    : I4xSystem instance which provides OS, rendering, and user context 
+        - xml       : Element tree of this Input element
+        - item_id   : id for this input element (assigned by capa_problem.LoncapProblem) - string
+        - track_url : URL used for tracking - string
+        - state     : a dictionary with optional keys: 
+                      * Value
+                      * ID
+                      * Status (answered, unanswered, unsubmitted)
+                      * Feedback (dictionary containing keys for hints, errors, or other 
+                        feedback from previous attempt)
+        - use        :
+        '''
+
         self.xml = xml
         self.tag = xml.tag
-        if not state:
-            state = {}
+        self.system = system
+        if not state: state = {}
+
         ## ID should only come from one place. 
         ## If it comes from multiple, we use state first, XML second, and parameter
         ## third. Since we don't make this guarantee, we can swap this around in 
         ## the future if there's a more logical order. 
-        if item_id:
-            self.id = item_id
-        if xml.get('id'):
-            self.id = xml.get('id')
-        if 'id' in state:
-            self.id = state['id']
-        self.system = system
+        if item_id:       self.id = item_id
+        if xml.get('id'): self.id = xml.get('id')
+        if 'id' in state: self.id = state['id']
 
         self.value = ''
         if 'value' in state:
             self.value = state['value']
 
         self.msg = ''
-        if 'feedback' in state and 'message' in state['feedback']:
-            self.msg = state['feedback']['message']
-
+        feedback = state.get('feedback')
+        if feedback is not None:
+            self.msg = feedback.get('message','')
+            self.hint = feedback.get('hint','')
+            self.hintmode = feedback.get('hintmode',None)
+            
+            # put hint above msg if to be displayed
+            if self.hintmode == 'always':
+                self.msg = self.hint + ('<br/.>' if self.msg else '') + self.msg
+ 
         self.status = 'unanswered'
         if 'status' in state:
             self.status = state['status']
diff --git a/common/lib/capa/responsetypes.py b/common/lib/capa/responsetypes.py
index 2de9e27893..5a5296d805 100644
--- a/common/lib/capa/responsetypes.py
+++ b/common/lib/capa/responsetypes.py
@@ -51,7 +51,7 @@ class StudentInputError(Exception):
 #
 # Main base class for CAPA responsetypes
 
-class GenericResponse(object):
+class LoncapaResponse(object):
     '''
     Base class for CAPA responsetypes.  Each response type (ie a capa question,
     which is part of a capa problem) is represented as a subclass,
@@ -60,22 +60,31 @@ class GenericResponse(object):
       - get_score           : evaluate the given student answers, and return a CorrectMap
       - get_answers         : provide a dict of the expected answers for this problem
       
+    Each subclass must also define the following attributes:
+
+      - response_tag         : xhtml tag identifying this response (used in auto-registering)
+
     In addition, these methods are optional:
 
-      - get_max_score       : if defined, this is called to obtain the maximum score possible for this question
-      - setup_response      : find and note the answer input field IDs for the response; called by __init__
-      - render_html         : render this Response as HTML (must return XHTML compliant string)
-      - __unicode__         : unicode representation of this Response
+      - get_max_score        : if defined, this is called to obtain the maximum score possible for this question
+      - setup_response       : find and note the answer input field IDs for the response; called by __init__
+      - check_hint_condition : check to see if the student's answers satisfy a particular condition for a hint to be displayed
+      - render_html          : render this Response as HTML (must return XHTML compliant string)
+      - __unicode__          : unicode representation of this Response
 
     Each response type may also specify the following attributes:
 
-      - max_inputfields     : (int) maximum number of answer input fields (checked in __init__ if not None)
-      - allowed_inputfields : list of allowed input fields (each a string) for this Response
-      - required_attributes : list of required attributes (each a string) on the main response XML stanza
+      - max_inputfields      : (int) maximum number of answer input fields (checked in __init__ if not None)
+      - allowed_inputfields  : list of allowed input fields (each a string) for this Response
+      - required_attributes  : list of required attributes (each a string) on the main response XML stanza
+      - hint_tag             : xhtml tag identifying hint associated with this response inside hintgroup
 
     '''
     __metaclass__=abc.ABCMeta # abc = Abstract Base Class
 
+    response_tag = None
+    hint_tag = None
+
     max_inputfields = None
     allowed_inputfields = []
     required_attributes = []
@@ -85,7 +94,7 @@ class GenericResponse(object):
         Init is passed the following arguments:
 
           - xml         : ElementTree of this Response
-          - inputfields : list of ElementTrees for each input entry field in this Response
+          - inputfields : ordered list of ElementTrees for each input entry field in this Response
           - context     : script processor context
           - system      : I4xSystem instance which provides OS, rendering, and user context 
 
@@ -112,7 +121,7 @@ class GenericResponse(object):
                 msg += "\nSee XML source line %s" % getattr(xml,'sourceline','<unavailable>')
                 raise LoncapaProblemError(msg)
 
-        self.answer_ids = [x.get('id') for x in self.inputfields]
+        self.answer_ids = [x.get('id') for x in self.inputfields]	# ordered list of answer_id values for this response
         if self.max_inputfields==1:
             self.answer_id = self.answer_ids[0]		# for convenience
 
@@ -140,8 +149,85 @@ class GenericResponse(object):
         tree.tail = self.xml.tail
         return tree
 
+    def evaluate_answers(self,student_answers,old_cmap):
+        '''
+        Called by capa_problem.LoncapaProblem to evaluate student answers, and to
+        generate hints (if any).
+
+        Returns the new CorrectMap, with (correctness,msg,hint,hintmode) for each answer_id.
+        '''
+        new_cmap = self.get_score(student_answers)
+        self.get_hints(student_answers, new_cmap, old_cmap)
+        return new_cmap
+
+    def get_hints(self, student_answers, new_cmap, old_cmap):
+        '''
+        Generate adaptive hints for this problem based on student answers, the old CorrectMap,
+        and the new CorrectMap produced by get_score.
+
+        Does not return anything.
+
+        Modifies new_cmap, by adding hints to answer_id entries as appropriate.
+        '''
+        hintgroup = self.xml.find('hintgroup')
+        if hintgroup is None: return
+
+        # hint specified by function?
+        hintfn = hintgroup.get('hintfn')
+        if hintfn:
+            '''
+            Hint is determined by a function defined in the <script> context; evaluate that function to obtain
+            list of hint, hintmode for each answer_id.
+
+            The function should take arguments (answer_ids, student_answers, new_cmap, old_cmap)
+            and it should modify new_cmap as appropriate.
+
+            We may extend this in the future to add another argument which provides a callback procedure
+            to a social hint generation system.
+
+            '''
+            if not hintfn in self.context:
+                msg = 'missing specified hint function %s in script context' % hintfn
+                msg += "\nSee XML source line %s" % getattr(self.xml,'sourceline','<unavailable>')
+                raise LoncapaProblemError(msg)
+
+            try:
+                self.context[hintfn](self.answer_ids, student_answers, new_cmap, old_cmap)
+            except Exception, err:
+                msg = 'Error %s in evaluating hint function %s' % (err,hintfn)
+                msg += "\nSee XML source line %s" % getattr(self.xml,'sourceline','<unavailable>')
+                raise ResponseError(msg)
+            return
+
+        # hint specified by conditions and text dependent on conditions (a-la Loncapa design)
+        # see http://help.loncapa.org/cgi-bin/fom?file=291
+        #
+        # Example:
+        #
+        # <formularesponse samples="x@-5:5#11" id="11" answer="$answer">
+        #   <textline size="25" />
+        #   <hintgroup>
+        #     <formulahint samples="x@-5:5#11" answer="$wrongans" name="inversegrad"></formulahint>
+        #     <hintpart on="inversegrad">
+        #       <text>You have inverted the slope in the question.  The slope is
+        #             (y2-y1)/(x2 - x1) you have the slope as (x2-x1)/(y2-y1).</text>
+        #     </hintpart>
+        #   </hintgroup>     
+        # </formularesponse>
+
+        if self.hint_tag is not None and hintgroup.find(self.hint_tag) is not None and hasattr(self,'check_hint_condition'):
+            rephints = hintgroup.findall(self.hint_tag)
+            hints_to_show = self.check_hint_condition(rephints,student_answers)
+            hintmode = hintgroup.get('mode','always')	# can be 'on_request' or 'always' (default)
+            for hintpart in hintgroup.findall('hintpart'):
+                if hintpart.get('on') in hints_to_show:
+                    hint_text = hintpart.find('text').text
+                    aid = self.answer_ids[-1]		# make the hint appear after the last answer box in this response
+                    new_cmap.set_hint_and_mode(aid,hint_text,hintmode)
+            log.debug('after hint: new_cmap = %s' % new_cmap)
+
     @abc.abstractmethod
-    def get_score(self, student_answers, old_cmap):
+    def get_score(self, student_answers):
         '''
         Return a CorrectMap for the answers expected vs given.  This includes
         (correctness, npoints, msg) for each answer_id.
@@ -161,6 +247,17 @@ class GenericResponse(object):
         '''
         pass
 
+    def check_hint_condition(self,hxml_set,student_answers):
+        '''
+        Return a list of hints to show.
+
+          - hxml_set        : list of Element trees, each specifying a condition to be satisfied for a named hint condition
+          - student_answers : dict of student answers
+
+        Returns a list of names of hint conditions which were satisfied.  Those are used to determine which hints are displayed.
+        '''
+        pass
+
     def setup_response(self):
         pass
 
@@ -169,7 +266,7 @@ class GenericResponse(object):
 
 #-----------------------------------------------------------------------------
 
-class MultipleChoiceResponse(GenericResponse):
+class MultipleChoiceResponse(LoncapaResponse):
     # TODO: handle direction and randomize
     snippets = [{'snippet': '''<multiplechoiceresponse direction="vertical" randomize="yes">
      <choicegroup type="MultipleChoice">
@@ -181,6 +278,7 @@ class MultipleChoiceResponse(GenericResponse):
     </multiplechoiceresponse>
     '''}]
 
+    response_tag = 'multiplechoiceresponse'
     max_inputfields = 1
     allowed_inputfields = ['choicegroup']
 
@@ -208,7 +306,7 @@ class MultipleChoiceResponse(GenericResponse):
                 else:
                     choice.set("name", "choice_"+choice.get("name"))
 
-    def get_score(self, student_answers, old_cmap):
+    def get_score(self, student_answers):
         '''
         grade student response.
         '''
@@ -222,6 +320,9 @@ class MultipleChoiceResponse(GenericResponse):
         return {self.answer_id:self.correct_choices}
 
 class TrueFalseResponse(MultipleChoiceResponse):
+
+    response_tag = 'truefalseresponse'
+
     def mc_setup_response(self):
         i=0
         for response in self.xml.xpath("choicegroup"):
@@ -233,7 +334,7 @@ class TrueFalseResponse(MultipleChoiceResponse):
                 else:
                     choice.set("name", "choice_"+choice.get("name"))
     
-    def get_score(self, student_answers, old_cmap):
+    def get_score(self, student_answers):
         correct = set(self.correct_choices)
         answers = set(student_answers.get(self.answer_id, []))
         
@@ -244,7 +345,7 @@ class TrueFalseResponse(MultipleChoiceResponse):
 
 #-----------------------------------------------------------------------------
 
-class OptionResponse(GenericResponse):
+class OptionResponse(LoncapaResponse):
     '''
     TODO: handle direction and randomize
     '''
@@ -253,12 +354,14 @@ class OptionResponse(GenericResponse):
         <optioninput options="('Up','Down')" correct="Down"><text>The location of the earth</text></optioninput>
     </optionresponse>'''}]
 
+    response_tag = 'optionresponse'
+    hint_tag = 'optionhint'
     allowed_inputfields = ['optioninput']
 
     def setup_response(self):
         self.answer_fields = self.inputfields
 
-    def get_score(self, student_answers, old_cmap):
+    def get_score(self, student_answers):
         # log.debug('%s: student_answers=%s' % (unicode(self),student_answers))
         cmap = CorrectMap()
         amap = self.get_answers()
@@ -276,8 +379,10 @@ class OptionResponse(GenericResponse):
 
 #-----------------------------------------------------------------------------
 
-class NumericalResponse(GenericResponse):
+class NumericalResponse(LoncapaResponse):
 
+    response_tag = 'numericalresponse'
+    hint_tag = 'numericalhint'
     allowed_inputfields = ['textline']
     required_attributes = ['answer']
     max_inputfields = 1
@@ -298,7 +403,7 @@ class NumericalResponse(GenericResponse):
         except Exception:
             self.answer_id = None
 
-    def get_score(self, student_answers, old_cmap):
+    def get_score(self, student_answers):
         '''Grade a numeric response '''
         student_answer = student_answers[self.answer_id]
         try:
@@ -319,7 +424,7 @@ class NumericalResponse(GenericResponse):
 
 #-----------------------------------------------------------------------------
 
-class CustomResponse(GenericResponse):
+class CustomResponse(LoncapaResponse):
     '''
     Custom response.  The python code to be run should be in <answer>...</answer>
     or in a <script>...</script>
@@ -358,6 +463,7 @@ def sympy_check2():
     <responseparam description="Numerical Tolerance" type="tolerance" default="0.00001" name="tol"/>
   </customresponse>'''}]
 
+    response_tag = 'customresponse'
     allowed_inputfields = ['textline','textbox']
 
     def setup_response(self):
@@ -402,7 +508,7 @@ def sympy_check2():
                 else:
                     self.code = answer.text
 
-    def get_score(self, student_answers, old_cmap):
+    def get_score(self, student_answers):
         '''
         student_answers is a dict with everything from request.POST, but with the first part
         of each key removed (the string before the first "_").
@@ -540,6 +646,8 @@ class SymbolicResponse(CustomResponse):
       </text>
     </problem>'''}]
 
+    response_tag = 'symbolicresponse'
+
     def setup_response(self):
         self.xml.set('cfn','symmath_check')
         code = "from symmath import *"
@@ -548,7 +656,7 @@ class SymbolicResponse(CustomResponse):
 
 #-----------------------------------------------------------------------------
 
-class ExternalResponse(GenericResponse):
+class ExternalResponse(LoncapaResponse):
     '''
     Grade the students input using an external server.
     
@@ -594,6 +702,7 @@ main()
     </answer>
   </externalresponse>'''}]
 
+    response_tag = 'externalresponse'
     allowed_inputfields = ['textline','textbox']
 
     def setup_response(self):
@@ -647,7 +756,7 @@ main()
 
         return rxml
 
-    def get_score(self, student_answers, old_cmap):
+    def get_score(self, student_answers):
         idset = sorted(self.answer_ids)
         cmap = CorrectMap()
         try:
@@ -707,7 +816,7 @@ main()
 
 #-----------------------------------------------------------------------------
 
-class FormulaResponse(GenericResponse):
+class FormulaResponse(LoncapaResponse):
     '''
     Checking of symbolic math response using numerical sampling.
     '''
@@ -729,6 +838,8 @@ class FormulaResponse(GenericResponse):
 
     </problem>'''}]
 
+    response_tag = 'formularesponse'
+    hint_tag = 'formulahint'
     allowed_inputfields = ['textline']
     required_attributes = ['answer']
     max_inputfields = 1
@@ -743,7 +854,7 @@ class FormulaResponse(GenericResponse):
                                            id=xml.get('id'))[0]
             self.tolerance = contextualize_text(self.tolerance_xml, context)
         except Exception:
-            self.tolerance = 0
+            self.tolerance = '0.00001'
 
         ts = xml.get('type')
         if ts is None:
@@ -757,11 +868,16 @@ class FormulaResponse(GenericResponse):
         else: # Default
             self.case_sensitive = False
 
-    def get_score(self, student_answers, old_cmap):
-        variables=self.samples.split('@')[0].split(',')
-        numsamples=int(self.samples.split('@')[1].split('#')[1])
+    def get_score(self, student_answers):
+        given = student_answers[self.answer_id]
+        correctness = self.check_formula(self.correct_answer, given, self.samples)
+        return CorrectMap(self.answer_id, correctness)
+
+    def check_formula(self,expected, given, samples):
+        variables=samples.split('@')[0].split(',')
+        numsamples=int(samples.split('@')[1].split('#')[1])
         sranges=zip(*map(lambda x:map(float, x.split(",")), 
-                         self.samples.split('@')[1].split('#')[0].split(':')))
+                         samples.split('@')[1].split('#')[0].split(':')))
 
         ranges=dict(zip(variables, sranges))
         for i in range(numsamples):
@@ -771,23 +887,26 @@ class FormulaResponse(GenericResponse):
                 value = random.uniform(*ranges[var])
                 instructor_variables[str(var)] = value
                 student_variables[str(var)] = value
-            instructor_result = evaluator(instructor_variables,dict(),self.correct_answer, cs = self.case_sensitive)
+            #log.debug('formula: instructor_vars=%s, expected=%s' % (instructor_variables,expected))
+            instructor_result = evaluator(instructor_variables,dict(),expected, cs = self.case_sensitive)
             try: 
-                #print student_variables,dict(),student_answers[self.answer_id]
-                student_result = evaluator(student_variables,dict(),
-                                           student_answers[self.answer_id], 
+                #log.debug('formula: student_vars=%s, given=%s' % (student_variables,given))
+                student_result = evaluator(student_variables,
+                                           dict(),
+                                           given, 
                                            cs = self.case_sensitive)
             except UndefinedVariable as uv:
+                log.debbug('formularesponse: undefined variable in given=%s' % given)
                 raise StudentInputError(uv.message+" not permitted in answer")
-            except:
+            except Exception, err:
                 #traceback.print_exc()
+                log.debug('formularesponse: error %s in formula' % err)
                 raise StudentInputError("Error in formula")
             if numpy.isnan(student_result) or numpy.isinf(student_result):
-                return CorrectMap(self.answer_id, "incorrect")
+                return "incorrect"
             if not compare_with_tolerance(student_result, instructor_result, self.tolerance):
-                return CorrectMap(self.answer_id, "incorrect")
- 
-        return CorrectMap(self.answer_id, "correct")
+                return "incorrect"
+        return "correct"
 
     def strip_dict(self, d):
         ''' Takes a dict. Returns an identical dict, with all non-word
@@ -799,13 +918,30 @@ class FormulaResponse(GenericResponse):
                     isinstance(d[k], numbers.Number)])
         return d
 
+    def check_hint_condition(self,hxml_set,student_answers):
+        given = student_answers[self.answer_id]
+        hints_to_show = []
+        for hxml in hxml_set:
+            samples = hxml.get('samples')
+            name = hxml.get('name')
+            correct_answer = contextualize_text(hxml.get('answer'),self.context)
+            try:
+                correctness = self.check_formula(correct_answer, given, samples)
+            except Exception,err:
+                correctness = 'incorrect'
+            if correctness=='correct':
+                hints_to_show.append(name)
+        log.debug('hints_to_show = %s' % hints_to_show)
+        return hints_to_show
+
     def get_answers(self):
         return {self.answer_id:self.correct_answer}
 
 #-----------------------------------------------------------------------------
 
-class SchematicResponse(GenericResponse):
+class SchematicResponse(LoncapaResponse):
 
+    response_tag = 'schematicresponse'
     allowed_inputfields = ['schematic']
 
     def setup_response(self):
@@ -817,7 +953,7 @@ class SchematicResponse(GenericResponse):
         else:
             self.code = answer.text
 
-    def get_score(self, student_answers, old_cmap):
+    def get_score(self, student_answers):
         from capa_problem import global_context
         submission = [json.loads(student_answers[k]) for k in sorted(self.answer_ids)]
         self.context.update({'submission':submission})
@@ -831,7 +967,7 @@ class SchematicResponse(GenericResponse):
 
 #-----------------------------------------------------------------------------
 
-class ImageResponse(GenericResponse):
+class ImageResponse(LoncapaResponse):
     """
     Handle student response for image input: the input is a click on an image,
     which produces an [x,y] coordinate pair.  The click is correct if it falls
@@ -847,13 +983,14 @@ class ImageResponse(GenericResponse):
       <imageinput src="image2.jpg" width="210" height="130" rectangle="(12,12)-(40,60)" />
     </imageresponse>'''}]
 
+    response_tag = 'imageresponse'
     allowed_inputfields = ['imageinput']
 
     def setup_response(self):
         self.ielements = self.inputfields
         self.answer_ids = [ie.get('id')  for ie in self.ielements]
 
-    def get_score(self, student_answers, old_cmap):
+    def get_score(self, student_answers):
         correct_map = CorrectMap()
         expectedset = self.get_answers()
 
@@ -884,3 +1021,10 @@ class ImageResponse(GenericResponse):
 
     def get_answers(self):
         return dict([(ie.get('id'),ie.get('rectangle')) for ie in self.ielements])
+
+#-----------------------------------------------------------------------------
+# TEMPORARY: List of all response subclasses
+# FIXME: To be replaced by auto-registration
+
+__all__ = [ NumericalResponse, FormulaResponse, CustomResponse, SchematicResponse, MultipleChoiceResponse, TrueFalseResponse, ExternalResponse, ImageResponse, OptionResponse, SymbolicResponse ]
+
diff --git a/common/lib/capa/util.py b/common/lib/capa/util.py
index 996f6c8dac..f1cc8f859e 100644
--- a/common/lib/capa/util.py
+++ b/common/lib/capa/util.py
@@ -7,6 +7,11 @@ from calc import evaluator, UndefinedVariable
 def compare_with_tolerance(v1, v2, tol):
     ''' Compare v1 to v2 with maximum tolerance tol
     tol is relative if it ends in %; otherwise, it is absolute
+
+     - v1    :  student result (number)
+     - v2    :  instructor result (number)
+     - tol   :  tolerance (string or number)
+
     '''
     relative = "%" in tol
     if relative: