diff --git a/src/ifcexpressparser/bootstrap.py b/src/ifcexpressparser/bootstrap.py
index 00936c2f4b..77e7f7131e 100644
--- a/src/ifcexpressparser/bootstrap.py
+++ b/src/ifcexpressparser/bootstrap.py
@@ -19,8 +19,14 @@
 
 import sys
 import string
+import operator
+import itertools
+
 from pyparsing import *
 
+try: from functools import reduce
+except: pass
+
 class Expression:
     def __init__(self, contents):
         self.contents = contents[0]
@@ -56,12 +62,12 @@ class Keyword:
 class Terminal:
     def __init__(self, contents):
         self.contents = contents[0]
-    def __repr__(self):
         s = self.contents
-        is_keyword = len(s) >= 4 and s[0::len(s)-1] == '""' and \
+        self.is_keyword = len(s) >= 4 and s[0::len(s)-1] == '""' and \
             all(c in alphanums+"_" for c in s[1:-1])
-        ty = "CaselessKeyword" if is_keyword else "CaselessLiteral"
-        return "%s(%s)" % (ty, s)
+    def __repr__(self):
+        ty = "CaselessKeyword" if self.is_keyword else "CaselessLiteral"
+        return "%s(%s)" % (ty, self.contents)
 
 
 LPAREN = Suppress("(")
@@ -94,16 +100,16 @@ grammar.ignore(HASH + restOfLine)
 
 express = grammar.parseFile(sys.argv[1])
 
-def find_keywords(expr, li = None):
+def find_bytype(expr, ty, li = None):
     if li is None: li = []
     if isinstance(expr, Term):
         expr = expr.contents
-    if isinstance(expr, Keyword):
-        li.append(repr(expr))
-        return li
+    if isinstance(expr, ty):
+        li.append(expr)
+        return set(li)
     elif isinstance(expr, Expression):
         for term in expr:
-            find_keywords(term, li)
+            find_bytype(term, ty, li)
     return set(li)
 
 actions = {
@@ -131,18 +137,22 @@ emitted = set()
 to_combine = set(["simple_id"])
 to_ignore = set(["where_clause", "supertype_constraint", "unique_clause"])
 statements = []
+    
+terminals = reduce(lambda x,y: x | y, (find_bytype(e, Terminal) for id, e in express))
+keywords = list(filter(operator.attrgetter('is_keyword'), terminals))
+negated_keywords = map(lambda s: "~%s" % s, keywords)
 
 while True:
     emitted_in_loop = set()
     for id, expr in express:
-        kws = find_keywords(expr)
+        kws = map(repr, find_bytype(expr, Keyword))
         found = [k in emitted for k in kws]
         if id in to_emit and all(found):
             emitted_in_loop.add(id)
             emitted.add(id)
             stmt = "(%s)" % expr
             if id in to_combine:
-                stmt = "originalTextFor(Combine%s)" % stmt
+                stmt = " + ".join(itertools.chain(negated_keywords, ("originalTextFor(Combine%s)" % stmt,)))
             if id in actions:
                 stmt = "%s.setParseAction(%s)" % (stmt, actions[id])
             statements.append("%s = %s" % (id, stmt))
diff --git a/src/ifcexpressparser/express.bnf b/src/ifcexpressparser/express.bnf
index 89acfd4fff..de40bfaf23 100644
--- a/src/ifcexpressparser/express.bnf
+++ b/src/ifcexpressparser/express.bnf
@@ -1,5 +1,3 @@
-# Taken from http://sourceforge.net/p/exp-engine/expresso/ci/master/tree/docs/iso-10303-11--2004.bnf
-
 ABS = "abs" .
 ABSTRACT = "abstract" .
 ACOS = "acos" .
@@ -202,7 +200,7 @@ constructed_types = enumeration_type | select_type .
 declaration = entity_decl | function_decl | procedure_decl | subtype_constraint_decl | type_decl .
 derived_attr = attribute_decl ":" parameter_type ":=" expression ";" .
 derive_clause = DERIVE derived_attr { derived_attr } .
-domain_rule = rule_label_id ":" expression .
+domain_rule = [ rule_label_id ":" ] expression .
 element = expression [ ":" repetition ] .
 entity_body = { explicit_attr } [ derive_clause ] [ inverse_clause ] [ unique_clause ] [ where_clause ] .
 entity_constructor = entity_ref "(" [ expression { "," expression } ] ")" .
@@ -334,7 +332,7 @@ type_label_id = simple_id .
 unary_op = "+" | "-" | NOT .
 underlying_type = constructed_types | concrete_types .
 unique_clause = UNIQUE unique_rule ";" { unique_rule ";" } .
-unique_rule = rule_label_id ":" referenced_attribute { "," referenced_attribute } .
+unique_rule = [ rule_label_id ":" ] referenced_attribute { "," referenced_attribute } .
 until_control = UNTIL logical_expression .
 use_clause = USE FROM schema_ref [ "(" named_type_or_rename { "," named_type_or_rename } ")" ] ";" .
 variable_id = simple_id .