diff --git a/source/book.adoc b/source/book.adoc
index 2119b49..e1c52b4 100644
--- a/source/book.adoc
+++ b/source/book.adoc
@@ -33,10 +33,17 @@ who answered my many questions,
 especially `cdepillabout`, `FedericoSchonborn`, `tejing` and `smkuehnhold`.
 Any mistakes in this book are my own, however.
 
+I would also like to thank Luca Bruno (aka Lethalman).
+Although I have never interacted with them personally,
+I learned a great deal from
+their series of tutorials called https://nixos.org/guides/nix-pills/[Nix pills].
+
 include::intro/main.adoc[leveloffset=+1]
 
 include::nix-language/main.adoc[leveloffset=+1]
 
+include::nixpkgs/main.adoc[leveloffset=+1]
+
 include::hello-flake/main-generated.adoc[leveloffset=+1]
 
 include::hello-flake-repo/main-generated.adoc[leveloffset=+1]
@@ -53,4 +60,11 @@ include::new-flake/main.adoc[leveloffset=+1]
 
 include::recipes/main.adoc[leveloffset=+1]
 
-// TODO Acknowledge and provide links to nix pills, nix reference manual
+// TODO Use curly quotation marks (smart quotes)
+// TODO Replace all references to "later" with proper cross-references.
+// TODO Write about lazy evaluation file:///home/amy/github/eolas/nix/nix-language.md#lazy-evaluation
+// TODO Write about currying and partial function application
+// TODO Cover assertions file:///home/amy/github/eolas/nix/nix-language.md#lazy-evaluation
+// TODO Cover fixed point file:///home/amy/github/eolas/nix/nix-language.md#fixed-point
+// TODO Cover any material in file:///home/amy/github/eolas/nix/nix.md that I haven't already covered
+// TODO Cover built-in constants file:///home/amy/github/eolas/nix/nix-language.md#built-in-constants
diff --git a/source/hello-flake-repo/main.adoc0 b/source/hello-flake-repo/main.adoc0
index 8eee556..07888f8 100644
--- a/source/hello-flake-repo/main.adoc0
+++ b/source/hello-flake-repo/main.adoc0
@@ -81,7 +81,7 @@ flake dependencies, (e.g., version number, branch, revision, hash), so
 that _anyone, anywhere, any time, can re-create the exact same
 environment that the original developer used._
 
-No more complaints of "`but it works on my machine!`". That is the
+No more complaints of "but it works on my machine!". That is the
 benefit of using flakes.
 
 ////
diff --git a/source/new-flake/main.adoc b/source/new-flake/main.adoc
index 312f325..5628bbc 100644
--- a/source/new-flake/main.adoc
+++ b/source/new-flake/main.adoc
@@ -1,11 +1,17 @@
 = A new flake from scratch
 
 At last we are ready to create a flake from scratch!
-The sections in this chapter are very similar;
+No matter what programming languages you normally use,
+I recommend that you start by reading the <<_bash>> section.
+In it, I start with an extremely simple flake, and show how to improve and extend it.
+
+The remaining sections in this chapter are very similar;
 read the one for your language of choice.
 If you're interested in a language that I haven't covered, feel free to suggest it by creating an
 https://codeberg.org/mhwombat/nix-book/issues[issue].
 
+include::bash-flake/main-generated.adoc[leveloffset=+1]
+
 include::haskell-flake/main-generated.adoc[leveloffset=+1]
 
 include::python-flake/main-generated.adoc[leveloffset=+1]
diff --git a/source/new-flake/python-flake/main.adoc0 b/source/new-flake/python-flake/main.adoc0
index 70ee33f..a809d92 100644
--- a/source/new-flake/python-flake/main.adoc0
+++ b/source/new-flake/python-flake/main.adoc0
@@ -65,22 +65,20 @@ $ python hello.py
 
 == Configuring setuptools
 
-Next, create a Python script to build the package. We'll use Python's
+Next, configure the package. We'll use Python's
 setuptools, but you can use other build tools. For more information on
 setuptools, see the
-https://packaging.python.org/en/latest/guides/distributing-packages-using-setuptools/[Python
-Packaging User Guide], especially the section on
-https://packaging.python.org/en/latest/guides/distributing-packages-using-setuptools/#setup-args[setup
-args].
+https://setuptools.pypa.io/en/latest/index.html[Setuptools documentation], especially the section on
+https://setuptools.pypa.io/en/latest/userguide/pyproject_config.html[pyproject.toml].
 
 ////
-$ curl https://codeberg.org/mhwombat/hello-flake-python/raw/branch/main/setup.py --silent --output setup.py
+$ curl https://codeberg.org/mhwombat/hello-flake-python/raw/branch/main/pyproject.toml --silent --output pyproject.toml
 ////
 
-[source,python,linenums]
-.setup.py
+[source,toml,linenums]
+.pyproject.toml
 ....
-$# cat setup.py
+$# cat pyproject.toml
 ....
 
 == Building the program manually (optional)
@@ -140,11 +138,15 @@ Let's start with the development shell. It seems logical to write
 something like the following.
 
 ....
-        devShells = rec {
+      devShells = forAllSupportedSystems (system:
+        let
+          pkgs = nixpkgsFor.${system};
+          pythonEnv = pkgs.python3.withPackages (ps: [ ps.build ]);
+        in {
           default = pkgs.mkShell {
-            packages = [ (python.withPackages (ps: with ps; [ build ])) ];
+              packages = [ pythonEnv ];
           };
-        };
+      });
 ....
 
 Note that we need the parentheses to prevent `python.withPackages` and
@@ -153,31 +155,30 @@ wanted to work with `virtualenv` and `pip` instead of `build`. We could
 write something like the following.
 
 ....
-        devShells = rec {
+      devShells = forAllSupportedSystems (system:
+        let
+          pkgs = nixpkgsFor.${system};
+          pythonEnv = pkgs.python3.withPackages (ps: [ ps.virtualenv ps.pip ]);
+        in {
           default = pkgs.mkShell {
-            packages = [
-              # Python plus helper tools
-              (python.withPackages (ps: with ps; [
-                virtualenv # Virtualenv
-                pip # The pip installer
-              ]))
-            ];
+              packages = [ pythonEnv ];
           };
-        };
+      });
 ....
 
 For the package builder, we can use the `buildPythonApplication`
 function.
 
 ....
-        packages = rec {
-          hello = python.pkgs.buildPythonApplication {
+       packages = forAllSupportedSystems (system:
+        let pkgs = nixpkgsFor.${system}; in rec {
+          hello-flake-python = pkgs.python3Packages.buildPythonApplication {
             name = "hello-flake-python";
-            buildInputs = with python.pkgs; [ pip ];
+            pyproject = true;
             src = ./.;
+            build-system = with pkgs.python3Packages; [ setuptools ];
           };
-          default = hello;
-        };
+      });
 ....
 
 If you put all the pieces together, your `flake.nix` should look
diff --git a/source/nix-language/argument-sets.adoc b/source/nix-language/argument-sets.adoc
index 3c42b71..4dc235c 100644
--- a/source/nix-language/argument-sets.adoc
+++ b/source/nix-language/argument-sets.adoc
@@ -19,6 +19,7 @@ the key names in the attribute set _pattern are separated by commas.
 Here's an example of a function that has an attribute set as an input parameter.
 
 [source]
+.Example
 ....
 nix-repl> greet = { first, last }: "Hello ${first} ${last}! May I call you ${first}?"
 
@@ -36,6 +37,7 @@ using the syntax `_name_ ? _value_`.
 This is illustrated below.
 
 [source]
+.Example
 ....
 nix-repl> greet = { first, last ? "whatever-your-lastname-is", topic ? "Nix" }: "Hello ${first} ${last}! May I call you ${first}? Are you enjoying learning ${topic}?"
 
@@ -52,6 +54,7 @@ A function can allow the caller to supply argument sets that contain "extra" val
 This is done with the special parameter `...`.
 
 [source]
+.Example
 ....
 nix-repl> formatName = { first, last, ... }: "${first} ${last}"
 ....
@@ -60,6 +63,7 @@ One reason for doing this is to allow the caller to pass the same argument set t
 even though each function may not need all of the values.
 
 [source]
+.Example
 ....
 nix-repl> person = { first="Joe"; last="Bloggs"; address="123 Main Street"; }
 
@@ -78,6 +82,7 @@ It can be convenient for a function to be able to reference the argument set as
 This is done using an _@-pattern_.
 
 [source]
+.Example
 ....
 nix-repl> formatPoint = p@{ x, y, ... }: builtins.toXML p
 
@@ -88,6 +93,7 @@ nix-repl> formatPoint { x=5; y=3; z=2; }
 Alternatively, the @-pattern can appear _after_ the argument set, as in the example below.
 
 [source]
+.Example
 ....
 nix-repl> formatPoint = { x, y, ... } @ p: builtins.toXML p
 ....
@@ -98,6 +104,7 @@ In the example below, the function `greet` passes its argument set, including th
 to the function `confirmAddress`.
 
 [source]
+.Example
 ....
 nix-repl> confirmAddress = { address, ... }: "Do you still live at ${address}?"
 
diff --git a/source/nix-language/attribute-sets.adoc b/source/nix-language/attribute-sets.adoc
index 0d5ec79..849e726 100644
--- a/source/nix-language/attribute-sets.adoc
+++ b/source/nix-language/attribute-sets.adoc
@@ -5,6 +5,7 @@
 The `.` operator selects an attribute from a set.
 
 [source]
+.Example
 ....
 nix-repl> animal = { name = { first = "Professor"; last = "Paws"; }; age = 10; species = "cat"; }
 
@@ -20,6 +21,7 @@ nix-repl> animal . name . first
 We can use the `?` operator to find out if a set has a particular attribute.
 
 [source]
+.Example
 ....
 nix-repl> animal ? species
 true
@@ -28,13 +30,31 @@ nix-repl> animal ? bicycle
 false
 ....
 
-== Modification
+== Union
 
-We can use the `//` operator to modify an attribute set.
-Recall that Nix values are immutable, so the result is a new value (the original is not modified).
+We can use the `//` operator to combine two attribute sets.
 Attributes in the right-hand set take preference.
 
 [source]
+.Example
+....
+nix-repl> a = { x = 7; y = "hello"; }
+
+nix-repl> b = { y = "wombat"; z = 3; }
+
+nix-repl> a // b
+{
+  x = 7;
+  y = "wombat";
+  z = 3;
+}
+....
+
+This is often used to "modify" one or more values in the set.
+Recall that Nix values are immutable, so the result is a new value (the original is not actually modified).
+
+[source]
+.Example
 ....
 nix-repl> animal // { species = "tiger"; }
 { age = 10; name = { ... }; species = "tiger"; }
@@ -47,6 +67,7 @@ An ordinary attribute set cannot refer to its own elements.
 To do this, you need a _recursive_ attribute set.
 
 [source]
+.Example
 ....
 nix-repl> { x = 3; y = 4*x; }
 error: undefined variable 'x'
@@ -70,6 +91,7 @@ For more information on these and other built-in functions, see the Nix Manual
 Get an alphabetical list of the keys.
 
 [source]
+.Example
 ....
 nix-repl> builtins.attrNames animal
 [ "age" "name" "species" ]
@@ -78,6 +100,7 @@ nix-repl> builtins.attrNames animal
 Get the values associated with each key, in alphabetical order by the key names.
 
 [source]
+.Example
 ....
 nix-repl> builtins.attrValues animal
 [ 10 "Professor Paws" "cat" ]
@@ -86,6 +109,7 @@ nix-repl> builtins.attrValues animal
 What value is associated with a key?
 
 [source]
+.Example
 ....
 nix-repl> builtins.getAttr "age" animal
 10
@@ -94,6 +118,7 @@ nix-repl> builtins.getAttr "age" animal
 Does the set have a value for a key?
 
 [source]
+.Example
 ....
 nix-repl> builtins.hasAttr "name" animal
 true
@@ -105,6 +130,7 @@ false
 Remove one or more keys and associated values from a set.
 
 [source]
+.Example
 ....
 nix-repl> builtins.removeAttrs animal [ "age" "species" ]
 { name = "Professor Paws"; }
@@ -113,7 +139,9 @@ nix-repl> builtins.removeAttrs animal [ "age" "species" ]
 Display an attribute set, including nested sets.
 
 [source]
+.Example
 ....
 nix-repl> builtins.toJSON animal
 "{\"age\":10,\"name\":{\"first\":\"Professor\",\"last\":\"Paws\"},\"species\":\"cat\"}"
 ....
+
diff --git a/source/nix-language/booleans.adoc b/source/nix-language/booleans.adoc
index a0c404d..23f0bf6 100644
--- a/source/nix-language/booleans.adoc
+++ b/source/nix-language/booleans.adoc
@@ -4,6 +4,7 @@ The usual boolean operators are available.
 Recall that earlier we set `a = 7` and `b = 3`.
 
 [source]
+.Example
 ....
 nix-repl> a == 7                     # equality test
 true
@@ -37,6 +38,7 @@ One operator that might be unfamiliar to you is _logical implication_, which use
 The expression `u -> v` is equivalent to `!u || v`.
 
 [source]
+.Example
 ....
 nix-repl> u = false
 
diff --git a/source/nix-language/dont-read.adoc b/source/nix-language/dont-read.adoc
index 9f84d68..05ce35f 100644
--- a/source/nix-language/dont-read.adoc
+++ b/source/nix-language/dont-read.adoc
@@ -28,4 +28,5 @@ Afterward, come back to this chapter and read it in more detail.
 While writing this book, I anticipated that readers would want to skip around,
 alternating between pure learning and learning-by-doing.
 I've tried to structure the book to support that;
-sometimes repeating information from earlier chapters that you might have skipped.
+providing extensive cross-references to earlier and later sections,
+and sometimes repeating information from earlier chapters that you might have skipped.
diff --git a/source/nix-language/functions.adoc b/source/nix-language/functions.adoc
index 5d14d9a..03c2523 100644
--- a/source/nix-language/functions.adoc
+++ b/source/nix-language/functions.adoc
@@ -8,6 +8,7 @@ where the _expression_ typically involves the _parameter_.
 Consider the following example.
 
 [source]
+.Example
 ....
 nix-repl> x: x + 1
 «lambda @ «string»:1:1»
@@ -17,6 +18,9 @@ We created a function that adds `1` to its input.
 However, it doesn't have a name, so we can't use it directly.
 Anonymous functions do have their uses, as we shall see shortly.
 
+// TODO Add a cross-reference to "shortly"
+// TODO Show that you can pass a function to a function
+
 Note that the message printed by the Nix REPL when we created the function uses the term _lambda_.
 This derives from a branch of mathematics called _lambda calculus_.
 Lambda calculus was the inspiration for most functional languages such as Nix.
@@ -25,6 +29,7 @@ Functional programmers often call anonymous functions "lambdas".
 The Nix REPL confirms that the expression `x: x + 1` defines a function.
 
 [source]
+.Example
 ....
 nix-repl> :t x: x + 1
 a function
@@ -37,6 +42,7 @@ Recall from <<type-lambda>> that functions can be treated like any other data ty
 In particular, we can assign it to a variable.
 
 [source]
+.Example
 ....
 nix-repl> f = x: x + 1
 
@@ -44,6 +50,8 @@ nix-repl> f
 «lambda @ «string»:1:2»
 ....
 
+// TODO Show that you can pass a function to a function
+
 Procedural languages such as C or Java often use parenthesis to apply a function to a value, e.g. `f(5)`.
 Nix, like lambda calculus and most functional languages, does not require parenthesis for function application.
 This reduces visual clutter when chaining a series of functions.
@@ -51,6 +59,7 @@ This reduces visual clutter when chaining a series of functions.
 Now that our function has a name, we can use it.
 
 [source]
+.Example
 ....
 nix-repl> f 5
 6
@@ -63,6 +72,7 @@ To define a calculation that requires more than one parameter,
 we create functions that return functions!
 
 [source]
+.Example
 ....
 nix-repl> add = a: (b: a+b)
 ....
@@ -77,6 +87,7 @@ I used parentheses to emphasise the inner function, but they aren't necessary.
 More commonly we would write the following.
 
 [source]
+.Example
 ....
 nix-repl> add = a: b: a+b
 ....
@@ -85,6 +96,7 @@ If we only supply one parameter to `add`, the result is a new function rather th
 Invoking a function without supplying all of the expected parameters is called _partial application_.
 
 [source]
+.Example
 ....
 nix-repl> add 3             # Returns a function that adds 3 to any input
 «lambda @ «string»:1:6»
@@ -93,6 +105,7 @@ nix-repl> add 3             # Returns a function that adds 3 to any input
 Now let's apply `add 3` to the value `5`.
 
 [source]
+.Example
 ....
 nix-repl> (add 3) 5
 8
@@ -101,6 +114,7 @@ nix-repl> (add 3) 5
 In fact, the parentheses aren't needed.
 
 [source]
+.Example
 ....
 nix-repl> add 3 5
 8
@@ -118,6 +132,7 @@ and returns a new function that takes a single parameter `b`, and returns the va
 Let's apply `add` to the value `3`, and give the resulting new function a name, `g`.
 
 [source]
+.Example
 ....
 nix-repl> g = add 3
 ....
@@ -126,6 +141,7 @@ The function `g` takes a single parameter and adds `3` to it.
 The Nix REPL confirms that `g` is indeed a function.
 
 [source]
+.Example
 ....
 nix-repl> :t g
 a function
@@ -134,6 +150,7 @@ a function
 Now we can apply `g` to a number to get a new number.
 
 [source]
+.Example
 ....
 nix-repl> g 5
 8