Implemented a first and basic version of a Rete rule engine

src/core/global_symbols.py

@@ -1,9 +1,17 @@
 # events
-EVENT_CONCEPT_PRECEDENCE_MODIFIED = "evt_cpm"
-EVENT_RULE_PRECEDENCE_MODIFIED = "evt_rpm"
-EVENT_CONTEXT_DISPOSED = "evt_cd"
-EVENT_USER_INPUT_EVALUATED = "evt_uie"
-EVENT_CONCEPT_CREATED = "evt_cc"
+
+EVENT_CONCEPT_PRECEDENCE_MODIFIED = "evt_cp_m"
+EVENT_RULE_PRECEDENCE_MODIFIED = "evt_rp_m"
+EVENT_CONTEXT_DISPOSED = "evt_ctx_d"
+EVENT_USER_INPUT_EVALUATED = "evt_ui_e"
+EVENT_CONCEPT_CREATED = "evt_c_c"
+EVENT_CONCEPT_DELETED = "evt_c_d"
+EVENT_CONCEPT_ID_DELETED = "evt_c_id_d"
+EVENT_RULE_CREATED = "evt_r_c"
+EVENT_RULE_DELETED = "evt_r_d"
+EVENT_RULE_ID_DELETED = "evt_r_id_d"
+EVENT_ONTOLOGY_CREATED = "evt_o_c"
+EVENT_ONTOLOGY_DELETED = "evt_o_d"
 
 # comparison context
 RULE_COMPARISON_CONTEXT = "Rule"
@@ -40,3 +48,10 @@ class RemovedType(CustomType):
 NotInit = NotInitType()
 NotFound = NotFoundType()
 Removed = RemovedType()
+
+
+class ErrorObj:
+    """
+    To indicate that somehow, the underlying object is (or has) an error
+    """
+    pass