diff --git a/src/cpl_query/enumerable/enumerable.py b/src/cpl_query/enumerable/enumerable.py
index 10a528ce..6291cd5d 100644
--- a/src/cpl_query/enumerable/enumerable.py
+++ b/src/cpl_query/enumerable/enumerable.py
@@ -206,21 +206,17 @@ class Enumerable(EnumerableABC):
         if _func is None:
             _func = _default_lambda
 
-        result = Enumerable()
-        result.extend(_func(_o) for _o in self)
-        return result
+        _l = [_func(_o) for _o in self]
+        return Enumerable(self._type if len(_l) < 1 else type(_l[0]), _l)
 
     def select_many(self, _func: Callable = None) -> EnumerableABC:
         if _func is None:
             _func = _default_lambda
 
-        result = Enumerable()
-        # The line below is pain. I don't understand anything of it...
+        # The line below is pain. I don't understand anything of the list comprehension...
         # written on 09.11.2022 by Sven Heidemann
-        elements = [_a for _o in self for _a in _func(_o)]
-
-        result.extend(elements)
-        return result
+        _l = [_a for _o in self for _a in _func(_o)]
+        return Enumerable(self._type if len(_l) < 1 else type(_l[0]), _l)
 
     def single(self: EnumerableABC) -> any:
         if self is None:
@@ -237,9 +233,9 @@ class Enumerable(EnumerableABC):
         if self is None:
             raise ArgumentNoneException(ExceptionArgument.list)
 
-        if len(self) > 1:
+        if self.count() > 1:
             raise IndexError('Found more than one element')
-        elif len(self) == 0:
+        elif self.count() == 0:
             return None
 
         return self.element_at(0)
diff --git a/src/cpl_query/iterable/iterable.py b/src/cpl_query/iterable/iterable.py
index 87f876de..154630cf 100644
--- a/src/cpl_query/iterable/iterable.py
+++ b/src/cpl_query/iterable/iterable.py
@@ -1,4 +1,4 @@
-from typing import Callable, Optional, Union
+from typing import Callable, Optional, Union, Iterable as IterableType
 
 from cpl_query._helper import is_number
 from cpl_query.exceptions import ArgumentNoneException, ExceptionArgument, InvalidTypeException, IndexOutOfRangeException
@@ -12,7 +12,7 @@ def _default_lambda(x: object):
 
 class Iterable(IterableABC):
 
-    def __init__(self, t: type = None, values: list = None):
+    def __init__(self, t: type = None, values: IterableType = None):
         IterableABC.__init__(self, t, values)
 
     def all(self, _func: Callable = None) -> bool:
diff --git a/src/cpl_query/iterable/iterable_abc.py b/src/cpl_query/iterable/iterable_abc.py
index 7b32ea90..b2b6ccc2 100644
--- a/src/cpl_query/iterable/iterable_abc.py
+++ b/src/cpl_query/iterable/iterable_abc.py
@@ -11,7 +11,7 @@ class IterableABC(SequenceABC, QueryableABC):
     """
 
     @abstractmethod
-    def __init__(self, t: type = None, values: list = None):
+    def __init__(self, t: type = None, values: Iterable = None):
         SequenceABC.__init__(self, t, values)
 
     def __getitem__(self, n) -> object:
diff --git a/unittests/unittests_query/enumerable_query_test_case.py b/unittests/unittests_query/enumerable_query_test_case.py
index 2f659abf..d95275e0 100644
--- a/unittests/unittests_query/enumerable_query_test_case.py
+++ b/unittests/unittests_query/enumerable_query_test_case.py
@@ -156,6 +156,8 @@ class EnumerableQueryTestCase(unittest.TestCase):
 
         self.assertEqual(len(res), len(results))
         self.assertEqual(res.element_at(0), s_res)
+        self.assertEqual(res.element_at(0), res.first())
+        self.assertEqual(res.first(), res.first())
 
     def test_first_or_default(self):
         results = []
diff --git a/unittests/unittests_query/iterable_query_test_case.py b/unittests/unittests_query/iterable_query_test_case.py
index a390e31c..c3618e17 100644
--- a/unittests/unittests_query/iterable_query_test_case.py
+++ b/unittests/unittests_query/iterable_query_test_case.py
@@ -151,6 +151,8 @@ class IterableQueryTestCase(unittest.TestCase):
 
         self.assertEqual(len(res), len(results))
         self.assertEqual(res[0], s_res)
+        self.assertEqual(res[0], res.first())
+        self.assertEqual(res.first(), res.first())
 
     def test_first_or_default(self):
         results = []
diff --git a/unittests/unittests_query/performance_test_case.py b/unittests/unittests_query/performance_test_case.py
new file mode 100644
index 00000000..1be52d01
--- /dev/null
+++ b/unittests/unittests_query/performance_test_case.py
@@ -0,0 +1,45 @@
+import sys
+import timeit
+import unittest
+
+from cpl_query.enumerable import Enumerable
+from cpl_query.extension.list import List
+from cpl_query.iterable import Iterable
+
+VALUES = 1000
+COUNT = 100
+
+
+class PerformanceTestCase(unittest.TestCase):
+
+    def setUp(self):
+        i = 0
+        self.values = []
+        while i < VALUES:
+            self.values.append(i)
+            i += 1
+
+    # def test_range(self):
+    #     default = timeit.timeit(lambda: list(self.values), number=COUNT)
+    #     enumerable = timeit.timeit(lambda: Enumerable(int, self.values), number=COUNT)
+    #     iterable = timeit.timeit(lambda: Iterable(int, self.values), number=COUNT)
+    #
+    #     print(f'd: {default}')
+    #     print(f'e: {enumerable}')
+    #     print(f'i: {iterable}')
+    #
+    #     self.assertLess(default, enumerable)
+    #     self.assertLess(default, iterable)
+
+    def test_where_single(self):
+        print(Enumerable(int, self.values).where(lambda x: x == COUNT).single_or_default())
+        # default = timeit.timeit(lambda: [x for x in list(self.values) if x == 50], number=COUNT)
+        # enumerable = timeit.timeit(lambda: Enumerable(int, self.values).where(lambda x: x == 50).single(), number=COUNT)
+        # iterable = timeit.timeit(lambda: Iterable(int, self.values).where(lambda x: x == 50).single(), number=COUNT)
+        #
+        # print(f'd: {default}')
+        # print(f'e: {enumerable}')
+        # print(f'i: {iterable}')
+        #
+        # self.assertLess(default, enumerable)
+        # self.assertLess(default, iterable)