Always create the "groups" set for new elements.

This allows a smaller initial knowledge base.

naive-nlu/tree_nlu/knowledge_evaluation.py

@@ -133,13 +133,13 @@ def pertenence_to_group(knowledge_base, elements, subj, group):
     group = resolve(knowledge_base, elements, group)
 
     if subj not in knowledge_base:
-        knowledge_base[subj] = {}
+        knowledge_base[subj] = {'groups': set()}
 
     if "groups" not in knowledge_base[subj]:
         knowledge_base[subj]["groups"] = set()
 
     if group not in knowledge_base:
-        knowledge_base[group] = {}
+        knowledge_base[group] = {'groups': set()}
 
     if "groups" not in knowledge_base[group]:
         knowledge_base[group]["groups"] = set()
@@ -179,7 +179,7 @@ def implies(knowledge_base, elements, precedent, consequent):
     consequent = resolve(knowledge_base, elements, consequent)
 
     if precedent not in knowledge_base:
-        knowledge_base[precedent] = {}
+        knowledge_base[precedent] = {'groups': set()}
 
     if "implications" not in knowledge_base[precedent]:
         knowledge_base[precedent]["implications"] = set()
@@ -197,7 +197,7 @@ def property_has_value(knowledge_base, elements, subj, prop, value):
     value = resolve(knowledge_base, elements, value)
 
     if subj not in knowledge_base:
-        knowledge_base[subj] = {}
+        knowledge_base[subj] = {'groups': set()}
 
     if prop not in knowledge_base[subj]:
         knowledge_base[subj][prop] = set()

naive-nlu/tree_nlu/tests/gac_100.py

@@ -648,33 +648,21 @@ base_knowledge = {
     'icecream': {
         "groups": {'noun', 'object', 'comestible', 'sweet'},
     },
-    'cold': {
-        "groups": {'property', 'temperature'},
-    },
     'hot': {
         "groups": {'property', 'temperature'},
     },
     'summer': {
         "groups": {'epoch'},
     },
-    'earth': {
-        "groups": {'noun', 'object', 'planet'},
-    },
     'planet': {
         "groups": {'noun', 'group'},
     },
-    'color': {
-        "groups": {'property', 'group'},
-    },
     'green': {
         "groups": {'noun', 'color', 'concept'},
     },
     'fly': {
         "groups": {'verb'},
     },
-    'chile': {
-        "groups": {'noun'},
-    },
 }
 
 def main():