Implemented a first and basic version of a Rete rule engine

tests/parsers/test_DefConceptParser.py

@@ -4,10 +4,11 @@ from dataclasses import dataclass
 import pytest
 from core.builtin_concepts import ParserResultConcept, BuiltinConcepts, ReturnValueConcept
 from core.concept import DEFINITION_TYPE_BNF, DEFINITION_TYPE_DEF, Concept, CV
+from core.global_symbols import NotInit
 from core.sheerka.services.SheerkaExecute import ParserInput
 from core.tokenizer import Keywords, Tokenizer, LexerError
 from parsers.BaseNodeParser import SCWC
-from parsers.BaseParser import NotInitializedNode, UnexpectedEofParsingError
+from parsers.BaseParser import UnexpectedEofParsingError
 from parsers.BnfNodeParser import OrderedChoice, ConceptExpression, StrMatch, Sequence
 from parsers.BnfDefinitionParser import BnfDefinitionParser
 from parsers.DefConceptParser import DefConceptParser, NameNode, SyntaxErrorNode
@@ -222,11 +223,11 @@ class TestDefConceptParser(TestUsingMemoryBasedSheerka):
         assert res.status
         assert sheerka.isinstance(parser_result, BuiltinConcepts.PARSER_RESULT)
         assert isinstance(node, DefConceptNode)
-        assert node.body == NotInitializedNode()
-        assert node.where == NotInitializedNode()
-        assert node.pre == NotInitializedNode()
-        assert node.post == NotInitializedNode()
-        assert node.ret == NotInitializedNode()
+        assert node.body is NotInit
+        assert node.where is NotInit
+        assert node.pre is NotInit
+        assert node.post is NotInit
+        assert node.ret is NotInit
 
     @pytest.mark.parametrize("part", [
         "as",