diff --git a/content/post/guards-guards.md b/content/post/guards-guards.md
new file mode 100644
index 0000000..efa507a
--- /dev/null
+++ b/content/post/guards-guards.md
@@ -0,0 +1,92 @@
++++
+date = 2026-06-27
+title = "Guards! Guards!"
+description = """
+Small gotcha about boolean operators in Elixir.
+"""
+
+[taxonomies]
+tags = [
+    "beam"
+]
++++
+
+Let's start with simple quiz.
+
+---
+
+Given module defined as:
+
+```elixir
+defmodule Foo do
+  def a(x) when is_integer(x) or is_map_key(x, :foo), do: true
+  def a(x), do: false
+
+  def b(x) when is_map_key(x, :foo) or is_integer(x), do: true
+  def b(x), do: false
+end
+```
+
+Try to answer these questions.
+
+{% question(
+    name="a-map",
+    desc="What will be result of `Foo.a(%{foo: 21})`?",
+    options = ["`true`", "`false`"],
+    correct = 0
+) %}
+This one is straightforward.
+
+We check guard, it has one condition `is_integer(x) or is_map_key(x, :foo)`.
+First one returns `false`, second returns `true`, Boolean's alternative results
+in `true` and first case is matched.
+{% end %}
+
+{% question(
+    name="a-int",
+    desc="What will be result of `Foo.a(37)`?",
+    options = ["`true`", "`false`"],
+    correct = 0
+) %}
+This one is straightforward as well.
+
+We check guard, it has one condition `is_integer(x) or is_map_key(x, :foo)`.
+First one returns `true`, second one isn't fired at all, because `or` operator
+is short circuiting.
+{% end %}
+
+{% question(
+    name="b-map",
+    desc="What will be result of `Foo.b(%{foo: 21})`?",
+    options = ["`true`", "`false`"],
+    correct = 0
+) %}
+Again, similar to the previous questions.
+
+We check guard, it has one condition `is_map_key(x, :foo) or is_integer(x)`.
+First one returns `true` and the rest is short circuited.
+{% end %}
+
+{% question(
+    name = "b-int",
+    desc = "What will be result of `Foo.b(37)`?",
+    options = ["`true`", "`false`"],
+    correct = 1
+) %}
+Ouch, something changed…
+
+Again, we check guard, one condition `is_map_key(x, :foo) or is_integer(x)`. We
+hit first clause `is_map_key(x, :foo)` and this **doesn't** return `false`,
+instead it fail. Failure in one of guard functions isn't converted to `false`
+but instead makes whole guard expression fail. This mean that `is_integer(x)`
+part will **never** be called.
+{% end %}
+
+---
+
+This behaviour is often surprising for a lot of Elixir developers, as it
+seemingly breaks commutative property of boolean operators. However, to be
+honest, these never were commutative because of short circuiting.
+
+It seems that Elixir at the time of writing (Elixir 1.20.1, OTP 29) do not warn
+about this issue.
diff --git a/sass/_quiz.scss b/sass/_quiz.scss
new file mode 100644
index 0000000..7e7ab50
--- /dev/null
+++ b/sass/_quiz.scss
@@ -0,0 +1,22 @@
+.question {
+  .answer {
+    display: none;
+    border: 1px solid pink;
+    padding: 1em;
+    margin: 2em 0;
+
+    .right { display: none; color: lightgreen; font-weight: 500; font-size: larger; }
+    .wrong { display: block; color: pink; font-weight: 500; font-size: larger; }
+  }
+
+  &:has(.option > input[type=radio]:checked) .answer {
+    display: block;
+  }
+
+  &:has(.option.correct > input[type=radio]:checked) .answer {
+    border-color: lightgreen;
+
+    .right { display: block; }
+    .wrong { display: none; }
+  }
+}
diff --git a/sass/style.scss b/sass/style.scss
index b2e0093..4fa10a6 100644
--- a/sass/style.scss
+++ b/sass/style.scss
@@ -7,6 +7,7 @@
 @import 'pagination';
 @import 'footer';
 @import 'rings';
+@import 'quiz';
 
 @media print {
   @import 'print';
diff --git a/templates/shortcodes/question.html b/templates/shortcodes/question.html
new file mode 100644
index 0000000..c8c52f9
--- /dev/null
+++ b/templates/shortcodes/question.html
@@ -0,0 +1,21 @@
+<div class="question" id="{{ name }}">
+  <p><b>Q:</b> {{ desc | markdown(inline=true) | safe }}</p>
+
+  {% for option in options %}
+  {% set id = name ~ "-a-" ~ loop.index %}
+  <div class="option {% if correct == loop.index0 %}correct{% endif %}">
+    <input type="radio"
+           name="{{name}}"
+           id="{{id}}"
+           value="{{option}}"
+           >
+    <label for="{{id}}">{{ option | markdown(inline=true) | safe }}</label>
+  </div>
+  {% endfor %}
+
+  <div class="answer">
+    <div class="wrong">WRONG</div>
+    <div class="right">RIGHT</div>
+    {{ body | markdown | safe }}
+  </div>
+</div>