diff --git a/doc/source/3_objects.rst b/doc/source/3_objects.rst
index 2e2bb95..b79bddc 100644
--- a/doc/source/3_objects.rst
+++ b/doc/source/3_objects.rst
@@ -615,9 +615,9 @@ observed that objects of some classes can be added. Is this true for
    In [3]: b = Polynomial((1,))     
 
    In [4]: a + b                                                                                                      
-   ---------------------------------------------------------------------------
-   TypeError                                 Traceback (most recent call last)
-   <ipython-input-4-bd58363a63fc> in <module>
+   --------------------------------------------------------------------------
+   TypeError                                Traceback (most recent call last)
+   Cell In [4], line 1
    ----> 1 a + b
 
    TypeError: unsupported operand type(s) for +: 'Polynomial' and 'Polynomial'
diff --git a/doc/source/fibonacci.rst b/doc/source/fibonacci.rst
index 208738d..f2fb4a4 100644
--- a/doc/source/fibonacci.rst
+++ b/doc/source/fibonacci.rst
@@ -12,6 +12,14 @@ fibonacci.fibonacci module
    :undoc-members:
    :show-inheritance:
 
+fibonacci.typesafe\_fibonacci module
+------------------------------------
+
+.. automodule:: fibonacci.typesafe_fibonacci
+   :members:
+   :undoc-members:
+   :show-inheritance:
+
 Module contents
 ---------------
 
diff --git a/doc/source/images/cover.pdf b/doc/source/images/cover.pdf
index 80634f6..bbb9faa 100644
Binary files a/doc/source/images/cover.pdf and b/doc/source/images/cover.pdf differ
diff --git a/doc/source/images/cover.png b/doc/source/images/cover.png
index acf7515..ccc0483 100644
Binary files a/doc/source/images/cover.png and b/doc/source/images/cover.png differ
diff --git a/doc/source/index.rst b/doc/source/index.rst
index aa63f56..da24724 100644
--- a/doc/source/index.rst
+++ b/doc/source/index.rst
@@ -28,11 +28,11 @@
    .. image:: images/cover.png
       :width: 10em
       :align: right
-      :target: https://www.amazon.co.uk/dp/B09NR9R9P3
+      :target: https://www.amazon.co.uk/dp/B0BRM69HKH
 
    The complete book text is available on this website. However, if you'd
    like to have a physical copy, then please `buy the book
-   <https://www.amazon.co.uk/dp/B09NR9R9P3>`__.
+   <https://www.amazon.co.uk/dp/B0BRM69HKH>`__.
 
 .. container:: preface
 
diff --git a/doc/webgit b/doc/webgit
index f73a645..fbded33 160000
--- a/doc/webgit
+++ b/doc/webgit
@@ -1 +1 @@
-Subproject commit f73a6456b63143502cb86bbd7eeef38e676f9f00
+Subproject commit fbded33d181d433fb6aea7ad5ff7af7247e93a37