diff --git a/src/core/sheerka/Sheerka.py b/src/core/sheerka/Sheerka.py
index 8a08851..2ac6fa7 100644
--- a/src/core/sheerka/Sheerka.py
+++ b/src/core/sheerka/Sheerka.py
@@ -799,9 +799,6 @@ class Sheerka(Concept):
         :return:
         """
 
-        if isinstance(a, BuiltinConcepts):  # common KSI error ;-)
-            raise SyntaxError("Remember that the first parameter of isinstance MUST be a concept")
-
         if not isinstance(a, Concept):
             return False
 
diff --git a/src/core/sheerka/services/SheerkaSetsManager.py b/src/core/sheerka/services/SheerkaSetsManager.py
index 17faa49..25e02fc 100644
--- a/src/core/sheerka/services/SheerkaSetsManager.py
+++ b/src/core/sheerka/services/SheerkaSetsManager.py
@@ -150,12 +150,7 @@ class SheerkaSetsManager(BaseService):
         :return:
         """
 
-        if isinstance(a, BuiltinConcepts):  # common KSI error ;-)
-            raise SyntaxError("Remember that the first parameter of isinstance MUST be a concept")
-
         ensure_concept(a, b)
-        # if not (isinstance(a, Concept) and isinstance(b, Concept)):
-        #     return False
 
         # TODO, first check the 'isa' property of a
         if not (a.id and b.id):
diff --git a/src/core/utils.py b/src/core/utils.py
index 0df61bb..01b496c 100644
--- a/src/core/utils.py
+++ b/src/core/utils.py
@@ -331,7 +331,10 @@ def unstr_concept(concept_repr):
     :param concept_repr:
     :return:
     """
-    if not (concept_repr and isinstance(concept_repr, str) and concept_repr.startswith("c:")):
+    if not (concept_repr and
+            isinstance(concept_repr, str) and
+            concept_repr.startswith("c:") and
+            concept_repr.endswith(":")):
         return None, None
 
     i = 2
diff --git a/tests/core/test_sheerka.py b/tests/core/test_sheerka.py
index 041135b..abd882f 100644
--- a/tests/core/test_sheerka.py
+++ b/tests/core/test_sheerka.py
@@ -4,7 +4,7 @@ import pytest
 from core.builtin_concepts import BuiltinConcepts, ReturnValueConcept, UserInputConcept
 from core.concept import Concept, PROPERTIES_TO_SERIALIZE, ConceptParts
 from core.sheerka.Sheerka import Sheerka, BASE_NODE_PARSER_CLASS
-from core.tokenizer import Token, TokenKind, Tokenizer
+from core.tokenizer import Token, TokenKind
 
 from tests.TestUsingFileBasedSheerka import TestUsingFileBasedSheerka
 from tests.TestUsingMemoryBasedSheerka import TestUsingMemoryBasedSheerka
@@ -276,30 +276,35 @@ class TestSheerkaUsingMemoryBasedSheerka(TestUsingMemoryBasedSheerka):
         assert not sheerka.is_success(sheerka.new(BuiltinConcepts.TOO_MANY_SUCCESS))
 
     @pytest.mark.parametrize("concept, expected", [
-        (None, None),
+        # by name
         ("foo", ["foo", "foo2"]),
         ("bar", "bar"),
         ("plus", "plus"),
         ("a mult b", "mult"),
-        ("unknown", None),
 
         # by tuple
-        ((None, None), None),
         (("foo", None), ["foo", "foo2"]),
         (("foo", "1002"), "foo2"),
         ((None, "1001"), "foo"),
         (("plus", None), "plus"),
         (("1001", None), "1001"),
-        (("unknown", None), None),
-        ((None, "unknown"), None),
-        #
+
         # by token
-        (Token(TokenKind.CONCEPT, (None, None), 0, 0, 0), None),
         (Token(TokenKind.CONCEPT, ("foo", None), 0, 0, 0), ["foo", "foo2"]),
 
         # by concept token str
         ("c:foo:", ["foo", "foo2"]),
+
+        # I cannot resolve
+        (None, None),
+        ("unknown", None),
+        ((None, None), None),
+        (("unknown", None), None),
+        ((None, "unknown"), None),
+        (Token(TokenKind.CONCEPT, (None, None), 0, 0, 0), None),
         ("c:unknown:", None),
+        ("c:foo:.id", None),
+        ("c:foo: + 1", None),
 
     ])
     def test_i_can_resolve_concept(self, concept, expected):
@@ -315,10 +320,8 @@ class TestSheerkaUsingMemoryBasedSheerka(TestUsingMemoryBasedSheerka):
         cmap = {k: concepts[i] for i, k in enumerate(["foo", "foo2", "bar", "plus", "mult", "1001"])}
         cmap[None] = None
 
-        if isinstance(expected, list):
-            assert sheerka.resolve(concept) == [cmap[e] for e in expected]
-        else:
-            assert sheerka.resolve(concept) == cmap[expected]
+        real_expected = [cmap[e] for e in expected] if isinstance(expected, list) else cmap[expected]
+        assert sheerka.resolve(concept) == real_expected
 
     def test_i_can_resolve_when_searching_by_definition(self):
         sheerka, context, plus = self.init_concepts(
@@ -328,6 +331,7 @@ class TestSheerkaUsingMemoryBasedSheerka(TestUsingMemoryBasedSheerka):
 
         assert sheerka.resolve("a plus b") == plus
 
+
 class TestSheerkaUsingFileBasedSheerka(TestUsingFileBasedSheerka):
 
     def test_root_folder_is_created_after_initialization(self):
diff --git a/tests/core/test_utils.py b/tests/core/test_utils.py
index 632b139..875846f 100644
--- a/tests/core/test_utils.py
+++ b/tests/core/test_utils.py
@@ -158,6 +158,7 @@ def test_i_can_escape():
     ("c:key|id:", "key", "id"),
     ("c:|id:", None, "id"),
     ("c:key|:", "key", None),
+    ("c:key|id:x", None, None),
 ])
 def test_i_can_unstr_concept(text, expected_key, expected_id):
     k, i = core.utils.unstr_concept(text)