diff --git a/TermTk/TTkCore/string.py b/TermTk/TTkCore/string.py
index 2fa81668..4ce0bc08 100644
--- a/TermTk/TTkCore/string.py
+++ b/TermTk/TTkCore/string.py
@@ -148,12 +148,12 @@ class TTkString():
         return complex(self._text)
 
     # Operators
-    def __lt__(self, other): return self._text <  other if type(other) is str else self._text <  other._text
-    def __le__(self, other): return self._text <= other if type(other) is str else self._text <= other._text
-    def __eq__(self, other): return self._text == other if type(other) is str else self._text == other._text
-    def __ne__(self, other): return self._text != other if type(other) is str else self._text != other._text
-    def __gt__(self, other): return self._text >  other if type(other) is str else self._text >  other._text
-    def __ge__(self, other): return self._text >= other if type(other) is str else self._text >= other._text
+    def __lt__(self, other): return self._text <  other._text if issubclass(type(other),TTkString) else self._text <  other
+    def __le__(self, other): return self._text <= other._text if issubclass(type(other),TTkString) else self._text <= other
+    def __eq__(self, other): return self._text == other._text if issubclass(type(other),TTkString) else self._text == other
+    def __ne__(self, other): return self._text != other._text if issubclass(type(other),TTkString) else self._text != other
+    def __gt__(self, other): return self._text >  other._text if issubclass(type(other),TTkString) else self._text >  other
+    def __ge__(self, other): return self._text >= other._text if issubclass(type(other),TTkString) else self._text >= other
 
     def isdigit(self):
         return self._text.isdigit()
diff --git a/tests/timeit/10.type.issubclass.py b/tests/timeit/10.type.issubclass.py
new file mode 100644
index 00000000..0af8d750
--- /dev/null
+++ b/tests/timeit/10.type.issubclass.py
@@ -0,0 +1,78 @@
+#!/usr/bin/env python3
+
+# MIT License
+#
+# Copyright (c) 2021 Eugenio Parodi <ceccopierangiolieugenio AT googlemail DOT com>
+#
+# Permission is hereby granted, free of charge, to any person obtaining a copy
+# of this software and associated documentation files (the "Software"), to deal
+# in the Software without restriction, including without limitation the rights
+# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+# copies of the Software, and to permit persons to whom the Software is
+# furnished to do so, subject to the following conditions:
+#
+# The above copyright notice and this permission notice shall be included in all
+# copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+# SOFTWARE.
+
+import sys, os
+
+import timeit
+import random
+import unicodedata
+
+sys.path.append(os.path.join(sys.path[0],'../..'))
+sys.path.append(os.path.join(sys.path[0],'.'))
+import TermTk as ttk
+
+class A(ttk.TTkString):pass
+class B(A):pass
+class C(B):pass
+
+c = C("Eugenio")
+s = ttk.TTkString("Eugenio")
+
+def test1(text): return 1 if type(c) is str else 0
+def test2(text): return 1 if type(c) == str else 0
+def test3(text): return 1 if issubclass(type(c), ttk.TTkString) else 0
+def test4(text): return 1 if c==s else 0
+def test5(text): return 1 if s==c else 0
+def test6(text): return 1 if c=='Eugenio' else 0
+
+loop = 20000
+
+
+a="123"
+result = timeit.timeit('test1(a)', globals=globals(), number=loop)
+print(f"1a  {result / loop:.10f} - {result / loop} {test1(a)}")
+result = timeit.timeit('test2(a)', globals=globals(), number=loop)
+print(f"2a  {result / loop:.10f} - {result / loop} {test2(a)}")
+result = timeit.timeit('test3(a)', globals=globals(), number=loop)
+print(f"3a  {result / loop:.10f} - {result / loop} {test3(a)}")
+result = timeit.timeit('test4(a)', globals=globals(), number=loop)
+print(f"4a  {result / loop:.10f} - {result / loop} {test4(a)}")
+result = timeit.timeit('test5(a)', globals=globals(), number=loop)
+print(f"5a  {result / loop:.10f} - {result / loop} {test5(a)}")
+result = timeit.timeit('test6(a)', globals=globals(), number=loop)
+print(f"6a  {result / loop:.10f} - {result / loop} {test6(a)}")
+
+a="456"
+result = timeit.timeit('test1(a)', globals=globals(), number=loop)
+print(f"1b  {result / loop:.10f} - {result / loop} {test1(a)}")
+result = timeit.timeit('test2(a)', globals=globals(), number=loop)
+print(f"2b  {result / loop:.10f} - {result / loop} {test2(a)}")
+result = timeit.timeit('test3(a)', globals=globals(), number=loop)
+print(f"3b  {result / loop:.10f} - {result / loop} {test3(a)}")
+result = timeit.timeit('test4(a)', globals=globals(), number=loop)
+print(f"4b  {result / loop:.10f} - {result / loop} {test4(a)}")
+result = timeit.timeit('test5(a)', globals=globals(), number=loop)
+print(f"5b  {result / loop:.10f} - {result / loop} {test5(a)}")
+result = timeit.timeit('test6(a)', globals=globals(), number=loop)
+print(f"6b  {result / loop:.10f} - {result / loop} {test6(a)}")
\ No newline at end of file