diff --git a/courseware/capa/calc.py b/courseware/capa/calc.py
index 571f4991d5..63c5c9de01 100644
--- a/courseware/capa/calc.py
+++ b/courseware/capa/calc.py
@@ -2,6 +2,7 @@ import copy
 import logging
 import math
 import operator
+import re
 
 import numpy
 import scipy.constants
@@ -10,7 +11,7 @@ from pyparsing import Word, alphas, nums, oneOf, Literal
 from pyparsing import ZeroOrMore, OneOrMore, StringStart
 from pyparsing import StringEnd, Optional, Forward
 from pyparsing import CaselessLiteral, Group, StringEnd
-from pyparsing import NoMatch, stringEnd
+from pyparsing import NoMatch, stringEnd, alphanums
 
 default_functions = {'sin' : numpy.sin, 
                      'cos' : numpy.cos, 
@@ -35,10 +36,40 @@ default_variables = {'j':numpy.complex(0,1),
 
 log = logging.getLogger("mitx.courseware.capa")
 
-def evaluator(variables, functions, string):
+class UndefinedVariable(Exception):
+    def raiseself(self):
+        ''' Helper so we can use inside of a lambda '''
+        raise self
+
+
+general_whitespace = re.compile('[^\w]+')
+def check_variables(string, variables):
+    '''  Confirm the only variables in string are defined.  
+
+    Pyparsing uses a left-to-right parser, which makes the more
+    elegant approach pretty hopeless. 
+
+    achar = reduce(lambda a,b:a|b ,map(Literal,alphas)) # Any alphabetic character
+    undefined_variable = achar + Word(alphanums)
+    undefined_variable.setParseAction(lambda x:UndefinedVariable("".join(x)).raiseself())
+    varnames = varnames | undefined_variable'''
+    possible_variables = re.split(general_whitespace, string) # List of all alnums in string
+    bad_variables = list()
+    for v in possible_variables:
+        if len(v) == 0:
+            continue
+        if v[0] <= '9' and '0' <= 'v': # Skip things that begin with numbers
+            continue
+        if v not in variables: 
+            bad_variables.append(v)
+    if len(bad_variables)>0:
+        raise UndefinedVariable(' '.join(bad_variables))
+
+def evaluator(variables, functions, string, cs=False):
     ''' Evaluate an expression. Variables are passed as a dictionary
     from string to value. Unary functions are passed as a dictionary
     from string to function. Variables must be floats.
+    cs: Case sensitive
 
     TODO: Fix it so we can pass integers and complex numbers in variables dict
     '''
@@ -51,6 +82,19 @@ def evaluator(variables, functions, string):
     all_functions = copy.copy(default_functions)
     all_functions.update(functions)
     
+    if not cs: 
+        string_cs = string.lower()
+        for v in all_variables.keys():
+            all_variables[v.lower()]=all_variables[v]
+        for f in all_functions.keys():
+            all_functions[f.lower()]=all_functions[f]
+        CasedLiteral = CaselessLiteral 
+    else:
+        string_cs = string
+        CasedLiteral = Literal
+
+    check_variables(string_cs, set(all_variables.keys()+all_functions.keys()))
+
     if string.strip() == "":
         return float('nan')
     ops = { "^" : operator.pow,
@@ -137,19 +181,19 @@ def evaluator(variables, functions, string):
         # We sort the list so that var names (like "e2") match before 
         # mathematical constants (like "e"). This is kind of a hack.
         all_variables_keys = sorted(all_variables.keys(), key=len, reverse=True)
-        varnames = sreduce(lambda x,y:x|y, map(lambda x: CaselessLiteral(x), all_variables_keys))
+        varnames = sreduce(lambda x,y:x|y, map(lambda x: CasedLiteral(x), all_variables_keys))
         varnames.setParseAction(lambda x:map(lambda y:all_variables[y], x))
     else:
         varnames=NoMatch()
     # Same thing for functions. 
     if len(all_functions)>0:
-        funcnames = sreduce(lambda x,y:x|y, map(lambda x: CaselessLiteral(x), all_functions.keys()))
+        funcnames = sreduce(lambda x,y:x|y, map(lambda x: CasedLiteral(x), all_functions.keys()))
         function = funcnames+lpar.suppress()+expr+rpar.suppress()
         function.setParseAction(func_parse_action)
     else:
         function = NoMatch()
 
-    atom = number | varnames | lpar+expr+rpar | function
+    atom = number | function | varnames | lpar+expr+rpar
     factor << (atom + ZeroOrMore(exp+atom)).setParseAction(exp_parse_action) # 7^6
     paritem = factor + ZeroOrMore(Literal('||')+factor) # 5k || 4k
     paritem=paritem.setParseAction(parallel)
diff --git a/courseware/capa/capa_problem.py b/courseware/capa/capa_problem.py
index 73ef168cf0..e9778008c1 100644
--- a/courseware/capa/capa_problem.py
+++ b/courseware/capa/capa_problem.py
@@ -15,7 +15,7 @@ from mako.template import Template
 
 from util import contextualize_text
 from inputtypes import textline, schematic
-from responsetypes import numericalresponse, formularesponse, customresponse, schematicresponse
+from responsetypes import numericalresponse, formularesponse, customresponse, schematicresponse, StudentInputError
 
 import calc
 import eia
diff --git a/courseware/capa/responsetypes.py b/courseware/capa/responsetypes.py
index 7f2b61e997..8809d935b1 100644
--- a/courseware/capa/responsetypes.py
+++ b/courseware/capa/responsetypes.py
@@ -3,8 +3,9 @@ import math
 import numpy
 import random
 import scipy
+import traceback
 
-from calc import evaluator
+from calc import evaluator, UndefinedVariable
 from django.conf import settings
 from util import contextualize_text
 
@@ -84,6 +85,9 @@ class customresponse(object):
         # be handled by capa_problem
         return {}
 
+class StudentInputError(Exception):
+    pass
+
 class formularesponse(object):
     def __init__(self, xml, context):
         self.xml = xml
@@ -95,6 +99,17 @@ class formularesponse(object):
         self.answer_id = xml.xpath('//*[@id=$id]//textline/@id',
                                    id=xml.get('id'))[0]
         self.context = context
+        ts = xml.get('type')
+        if ts == None:
+            typeslist = []
+        else:
+            typeslist = ts.split(',')
+        if 'ci' in typeslist: # Case insensitive
+            self.case_sensitive = False
+        elif 'cs' in typeslist: # Case sensitive
+            self.case_sensitive = True
+        else: # Default
+            self.case_sensitive = False
 
 
     def grade(self, student_answers):
@@ -113,7 +128,16 @@ class formularesponse(object):
                 instructor_variables[str(var)] = value
                 student_variables[str(var)] = value
             instructor_result = evaluator(instructor_variables,dict(),self.correct_answer)
-            student_result = evaluator(student_variables,dict(),student_answers[self.answer_id])
+            try: 
+                #print student_variables,dict(),student_answers[self.answer_id]
+                student_result = evaluator(student_variables,dict(),
+                                           student_answers[self.answer_id], 
+                                           cs = self.case_sensitive)
+            except UndefinedVariable as uv:
+                raise StudentInputError('Undefined: '+uv.message)
+            except:
+                #traceback.print_exc()
+                raise StudentInputError("Syntax Error")
             if math.isnan(student_result) or math.isinf(student_result):
                 return {self.answer_id:"incorrect"}
             if not compare_with_tolerance(student_result, instructor_result, self.tolerance):
diff --git a/courseware/modules/capa_module.py b/courseware/modules/capa_module.py
index 378c322c42..366d0463e4 100644
--- a/courseware/modules/capa_module.py
+++ b/courseware/modules/capa_module.py
@@ -21,7 +21,7 @@ from mitxmako.shortcuts import render_to_response, render_to_string
 from django.http import Http404
 
 from x_module import XModule
-from courseware.capa.capa_problem import LoncapaProblem
+from courseware.capa.capa_problem import LoncapaProblem, StudentInputError
 import courseware.content_parser as content_parser
 
 log = logging.getLogger("mitx.courseware")
@@ -94,6 +94,10 @@ class Module(XModule):
         if self.max_attempts != None: 
             attempts_str = " ({a}/{m})".format(a=self.attempts, m=self.max_attempts)
 
+        # We don't need a "save" button if infinite number of attempts and non-randomized
+        if self.max_attempts == None and self.rerandomize == False:
+            save_button = False
+
         # Check if explanation is available, and if so, give a link
         explain=""
         if self.lcp.done and self.explain_available=='attempted':
@@ -277,22 +281,27 @@ class Module(XModule):
             lcp_id = self.lcp.problem_id
             filename = self.lcp.filename
             correct_map = self.lcp.grade_answers(answers)
+        except StudentInputError as inst: 
+            self.lcp = LoncapaProblem(filename, id=lcp_id, state=old_state)
+            traceback.print_exc()
+#            print {'error':sys.exc_info(),
+#                   'answers':answers, 
+#                   'seed':self.lcp.seed, 
+#                   'filename':self.lcp.filename}
+            return json.dumps({'success':inst.message})
         except: 
             self.lcp = LoncapaProblem(filename, id=lcp_id, state=old_state)
             traceback.print_exc()
-            print {'error':sys.exc_info(),
-                   'answers':answers, 
-                   'seed':self.lcp.seed, 
-                   'filename':self.lcp.filename}
-            return json.dumps({'success':'syntax'})
+            return json.dumps({'success':'Unknown Error'})
+            
 
         self.attempts = self.attempts + 1
         self.lcp.done=True
 
-        success = 'finished'
+        success = 'correct'
         for i in correct_map:
             if correct_map[i]!='correct':
-                success = 'errors'
+                success = 'incorrect'
 
         js=json.dumps({'correct_map' : correct_map,
                        'success' : success})
diff --git a/courseware/tests.py b/courseware/tests.py
index 39edcc0e72..b0d7cad19f 100644
--- a/courseware/tests.py
+++ b/courseware/tests.py
@@ -32,8 +32,22 @@ class ModelsTest(unittest.TestCase):
         self.assertTrue(abs(calc.evaluator(variables, functions, "k*T/q-0.025"))<0.001)
         exception_happened = False
         try: 
-            evaluator({},{}, "5+7 QWSEKO")
+            calc.evaluator({},{}, "5+7 QWSEKO")
         except:
             exception_happened = True
         self.assertTrue(exception_happened)
-            
+
+        try: 
+            calc.evaluator({'r1':5},{}, "r1+r2")
+        except calc.UndefinedVariable:
+            pass
+        
+        self.assertEqual(calc.evaluator(variables, functions, "r1*r3"), 8.0)
+
+        exception_happened = False
+        try: 
+            calc.evaluator(variables, functions, "r1*r3", cs=True)
+        except:
+            exception_happened = True
+        self.assertTrue(exception_happened)
+