diff --git a/README.md b/README.md
index 0009fc7..d03d436 100644
--- a/README.md
+++ b/README.md
@@ -1154,17 +1154,13 @@ class MyOpen():
 Hello World!
 ```
 
-#### Context managers:
+#### List of existing context managers:
 ```python
 with open('<path>', ...) as file: ...
 with wave.open('<path>', ...) as wave_file: ...
 with memoryview(<bytes/bytearray/array>) as view: ...
-```
-
-#### Reusable context managers:
-```python
+db = sqlite3.connect('<path>'); with db: db.execute('<insert_query>')
 lock = threading.RLock(); with lock: ...
-con  = sqlite3.connect('<path>'); with con: con.execute('<insert_query>')
 ```
 
 
@@ -1232,6 +1228,7 @@ class MySequence:
 * **It's a richer interface than the basic sequence.**
 * **Extending it generates iter(), contains(), reversed(), index(), and count().**
 * **Unlike `'abc.Iterable'` and `'abc.Collection'`, it is not a duck type. That is why `'issubclass(MySequence, collections.abc.Sequence)'` would return 'False' even if it had all the methods defined.**
+
 ```python
 class MyAbcSequence(collections.abc.Sequence):
     def __init__(self, a):
@@ -1258,6 +1255,8 @@ class MyAbcSequence(collections.abc.Sequence):
 +------------+----------+------------+----------+--------------+
 ```
 
+* **Other useful ABCs that automatically generate missing methods are: MutableSequence, Set, MutableSet, Mapping and MutableMapping.**
+
 
 Enum
 ----
diff --git a/index.html b/index.html
index bdd009b..4460f54 100644
--- a/index.html
+++ b/index.html
@@ -1075,14 +1075,12 @@ Z = dataclasses.make_dataclass(<span class="hljs-string">'Z'</span>, [<span clas
 <span class="hljs-meta">... </span>    print(file.read())
 Hello World!
 </code></pre>
-<h4 id="contextmanagers">Context managers:</h4>
+<h4 id="listofexistingcontextmanagers">List of existing context managers:</h4>
 <pre><code class="python language-python hljs"><span class="hljs-keyword">with</span> open(<span class="hljs-string">'&lt;path&gt;'</span>, ...) <span class="hljs-keyword">as</span> file: ...
 <span class="hljs-keyword">with</span> wave.open(<span class="hljs-string">'&lt;path&gt;'</span>, ...) <span class="hljs-keyword">as</span> wave_file: ...
 <span class="hljs-keyword">with</span> memoryview(&lt;bytes/bytearray/array&gt;) <span class="hljs-keyword">as</span> view: ...
-</code></pre>
-<h4 id="reusablecontextmanagers">Reusable context managers:</h4>
-<pre><code class="python language-python hljs">lock = threading.RLock(); <span class="hljs-keyword">with</span> lock: ...
-con  = sqlite3.connect(<span class="hljs-string">'&lt;path&gt;'</span>); <span class="hljs-keyword">with</span> con: con.execute(<span class="hljs-string">'&lt;insert_query&gt;'</span>)
+db = sqlite3.connect(<span class="hljs-string">'&lt;path&gt;'</span>); <span class="hljs-keyword">with</span> db: db.execute(<span class="hljs-string">'&lt;insert_query&gt;'</span>)
+lock = threading.RLock(); <span class="hljs-keyword">with</span> lock: ...
 </code></pre>
 <h2 id="iterableducktypes"><a href="#iterableducktypes" name="iterableducktypes">#</a>Iterable Duck Types</h2>
 <h3 id="iterable">Iterable</h3>
@@ -1168,6 +1166,9 @@ con  = sqlite3.connect(<span class="hljs-string">'&lt;path&gt;'</span>); <span c
 ┃ count()    │          │            │          │      ✓       ┃
 ┗━━━━━━━━━━━━┷━━━━━━━━━━┷━━━━━━━━━━━━┷━━━━━━━━━━┷━━━━━━━━━━━━━━┛
 </code></pre>
+<ul>
+<li><strong>Other useful ABCs that automatically generate missing methods are: MutableSequence, Set, MutableSet, Mapping and MutableMapping.</strong></li>
+</ul>
 <h2 id="enum"><a href="#enum" name="enum">#</a>Enum</h2>
 <pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> enum <span class="hljs-keyword">import</span> Enum, auto