Fixed #101 : Implement PLURIAL

Fixed #103 : Implement PlurialNodeParser
Fixed #104 : Implement dynamic concept
Fixed #107 : PrepareEvalxxxEvaluator: context hints are lost on a second evaluation

tests/core/test_SheerkaIsAManager.py

@@ -116,7 +116,8 @@ class TestSheerkaIsAManager(TestUsingMemoryBasedSheerka):
 
         context.add_to_private_hints(BuiltinConcepts.EVAL_GLOBAL_TRUTH_REQUESTED)
 
-        sheerka.set_isa(context, blue_instance, color)
+        res = sheerka.set_isa(context, blue_instance, color)
+        assert res.status
         assert sheerka.isa(blue_instance, color)
         assert sheerka.isaset(context, color)
         assert sheerka.isinset(blue_instance, color)
@@ -423,6 +424,20 @@ class TestSheerkaIsAManager(TestUsingMemoryBasedSheerka):
         foo = sheerka.get_by_id(foo.id)
         assert not sheerka.isa(foo, group2)
 
+    def test_i_can_set_isa_twice_when_global_truth_is_true_the_second_time(self):
+        sheerka, context, blue, color = self.init_concepts(Concept("blue"), Concept("color"))
+        global_truth_context = self.get_context(sheerka, global_truth=True)
+
+        blue_instance = sheerka.new("blue")
+        sheerka.set_isa(context, blue_instance, color)
+
+        # set it again with global_truth = True
+        res = sheerka.set_isa(global_truth_context, blue_instance, color)
+
+        assert res.status
+        assert sheerka.isa(blue_instance, color)
+        assert sheerka.isa(sheerka.new("blue"), color)  # try another instance
+
 
 class TestSheerkaSetsManagerUsingFileBasedSheerka(TestUsingFileBasedSheerka):
     def test_i_can_add_concept_to_set_and_retrieve_it_in_another_session(self):