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diff --git a/docs/lectures/03-datatypes.html b/docs/lectures/03-datatypes.html
@@ -1200,10 +1200,30 @@ <h2 id="polymorphic-functions-over-polymorphic-data">Polymorphic Functions over
 <span id="cb59-2"><a href="#cb59-2" aria-hidden="true" tabindex="-1"></a><span class="dt">Cons</span> <span class="dv">1</span> (<span class="dt">Cons</span> <span class="dv">2</span> (<span class="dt">Cons</span> <span class="dv">3</span> <span class="dt">Nil</span>))</span>
 <span id="cb59-3"><a href="#cb59-3" aria-hidden="true" tabindex="-1"></a></span>
 <span id="cb59-4"><a href="#cb59-4" aria-hidden="true" tabindex="-1"></a><span class="op">&gt;&gt;&gt;</span> append (<span class="dt">Cons</span> <span class="ch">'a'</span> (<span class="dt">Cons</span> <span class="ch">'b'</span> <span class="dt">Nil</span>)) (<span class="dt">Cons</span> <span class="ch">'c'</span> <span class="dt">Nil</span>)  <span class="co">-- a = Char</span></span>
-<span id="cb59-5"><a href="#cb59-5" aria-hidden="true" tabindex="-1"></a><span class="dt">Cons</span> <span class="ch">'a'</span> (<span class="dt">Cons</span> <span class="ch">'b'</span> (<span class="dt">Cons</span> <span class="ch">'c'</span> <span class="dt">Nil</span>))</span>
-<span id="cb59-6"><a href="#cb59-6" aria-hidden="true" tabindex="-1"></a></span>
-<span id="cb59-7"><a href="#cb59-7" aria-hidden="true" tabindex="-1"></a><span class="op">&gt;&gt;&gt;</span> append (<span class="dt">Cons</span> <span class="fl">1.1</span> (<span class="dt">Cons</span> <span class="fl">2.2</span> <span class="dt">Nil</span>)) (<span class="dt">Cons</span> <span class="ch">'a'</span> <span class="dt">Nil</span>)  <span class="co">-- a = ?</span></span>
-<span id="cb59-8"><a href="#cb59-8" aria-hidden="true" tabindex="-1"></a><span class="op">???</span></span></code></pre></div>
+<span id="cb59-5"><a href="#cb59-5" aria-hidden="true" tabindex="-1"></a><span class="dt">Cons</span> <span class="ch">'a'</span> (<span class="dt">Cons</span> <span class="ch">'b'</span> (<span class="dt">Cons</span> <span class="ch">'c'</span> <span class="dt">Nil</span>))</span></code></pre></div>
+<p><br>
+<br>
+<br>
+<br>
+<br>
+<br>
+<br>
+<br>
+<br>
+<br>
+<br>
+<br>
+<br>
+<br></p>
+<h2 id="quiz-6">QUIZ</h2>
+<p>With the type of <code class="sourceCode haskell">append</code> defined as</p>
+<p><code class="sourceCode haskell"><span class="ot">append ::</span> <span class="dt">List</span> a <span class="ot">-&gt;</span> <span class="dt">List</span> a <span class="ot">-&gt;</span> <span class="dt">List</span> a</code></p>
+<p>what would be result of</p>
+<div class="sourceCode" id="cb60"><pre class="sourceCode haskell"><code class="sourceCode haskell"><span id="cb60-1"><a href="#cb60-1" aria-hidden="true" tabindex="-1"></a>append (<span class="dt">Cons</span> <span class="ch">'a'</span> (<span class="dt">Cons</span> <span class="ch">'b'</span> <span class="dt">Nil</span>)) (<span class="dt">Cons</span> <span class="dt">True</span> <span class="dt">Nil</span>)</span></code></pre></div>
+<p><strong>A.</strong> <code class="sourceCode haskell"><span class="dt">Cons</span> <span class="ch">'a'</span> (<span class="dt">Cons</span> <span class="ch">'b'</span> (<span class="dt">Cons</span> <span class="dt">True</span> <span class="dt">Nil</span>))</code></p>
+<p><strong>B.</strong> <code class="sourceCode haskell"><span class="dt">Cons</span> <span class="ch">'a'</span> (<span class="dt">Cons</span> <span class="ch">'b'</span> <span class="dt">Nil</span>)</code></p>
+<p><strong>C.</strong> Type error</p>
+<p><em>Answer:</em> C</p>
 <p><br>
 <br>
 <br>
@@ -1220,18 +1240,18 @@ <h2 id="polymorphic-functions-over-polymorphic-data">Polymorphic Functions over
 <br></p>
 <h2 id="built-in-lists">Built-in Lists?</h2>
 <p>This is exactly how Haskell’s “built-in” lists are defined:</p>
-<div class="sourceCode" id="cb60"><pre class="sourceCode haskell"><code class="sourceCode haskell"><span id="cb60-1"><a href="#cb60-1" aria-hidden="true" tabindex="-1"></a><span class="kw">data</span> [a]    <span class="ot">=</span> [] <span class="op">|</span> (<span class="op">:</span>) a [a]</span>
-<span id="cb60-2"><a href="#cb60-2" aria-hidden="true" tabindex="-1"></a></span>
-<span id="cb60-3"><a href="#cb60-3" aria-hidden="true" tabindex="-1"></a><span class="kw">data</span> <span class="dt">List</span> a <span class="ot">=</span> <span class="dt">Nil</span> <span class="op">|</span> <span class="dt">Cons</span> a (<span class="dt">List</span> a)</span></code></pre></div>
+<div class="sourceCode" id="cb61"><pre class="sourceCode haskell"><code class="sourceCode haskell"><span id="cb61-1"><a href="#cb61-1" aria-hidden="true" tabindex="-1"></a><span class="kw">data</span> [a]    <span class="ot">=</span> [] <span class="op">|</span> (<span class="op">:</span>) a [a]</span>
+<span id="cb61-2"><a href="#cb61-2" aria-hidden="true" tabindex="-1"></a></span>
+<span id="cb61-3"><a href="#cb61-3" aria-hidden="true" tabindex="-1"></a><span class="kw">data</span> <span class="dt">List</span> a <span class="ot">=</span> <span class="dt">Nil</span> <span class="op">|</span> <span class="dt">Cons</span> a (<span class="dt">List</span> a)</span></code></pre></div>
 <ul>
 <li><code class="sourceCode haskell"><span class="dt">Nil</span></code> is called <code class="sourceCode haskell">[]</code></li>
 <li><code class="sourceCode haskell"><span class="dt">Cons</span></code> is called <code class="sourceCode haskell"><span class="op">:</span></code></li>
 </ul>
 <p>Many list manipulating functions e.g. in <code class="sourceCode haskell"><span class="dt">Data.List</span></code> are <em>polymorphic</em>
 - Can be reused across all kinds of lists.</p>
-<div class="sourceCode" id="cb61"><pre class="sourceCode haskell"><code class="sourceCode haskell"><span id="cb61-1"><a href="#cb61-1" aria-hidden="true" tabindex="-1"></a><span class="ot">(++) ::</span> [a] <span class="ot">-&gt;</span> [a] <span class="ot">-&gt;</span> [a]</span>
-<span id="cb61-2"><a href="#cb61-2" aria-hidden="true" tabindex="-1"></a><span class="fu">head</span><span class="ot"> ::</span> [a] <span class="ot">-&gt;</span> a</span>
-<span id="cb61-3"><a href="#cb61-3" aria-hidden="true" tabindex="-1"></a><span class="fu">tail</span><span class="ot"> ::</span> [a] <span class="ot">-&gt;</span> [a]</span></code></pre></div>
+<div class="sourceCode" id="cb62"><pre class="sourceCode haskell"><code class="sourceCode haskell"><span id="cb62-1"><a href="#cb62-1" aria-hidden="true" tabindex="-1"></a><span class="ot">(++) ::</span> [a] <span class="ot">-&gt;</span> [a] <span class="ot">-&gt;</span> [a]</span>
+<span id="cb62-2"><a href="#cb62-2" aria-hidden="true" tabindex="-1"></a><span class="fu">head</span><span class="ot"> ::</span> [a] <span class="ot">-&gt;</span> a</span>
+<span id="cb62-3"><a href="#cb62-3" aria-hidden="true" tabindex="-1"></a><span class="fu">tail</span><span class="ot"> ::</span> [a] <span class="ot">-&gt;</span> [a]</span></code></pre></div>
 <p><br>
 <br>
 <br>

diff --git a/lectures/03-datatypes.md b/lectures/03-datatypes.md
@@ -1416,11 +1416,45 @@ Cons 1 (Cons 2 (Cons 3 Nil))
 
 >>> append (Cons 'a' (Cons 'b' Nil)) (Cons 'c' Nil)  -- a = Char
 Cons 'a' (Cons 'b' (Cons 'c' Nil))
+```
 
->>> append (Cons 1.1 (Cons 2.2 Nil)) (Cons 'a' Nil)  -- a = ?
-???
+<br>
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+<br>
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+<br>
+<br>
+<br>
+<br>
+<br>
+<br>
+<br>
+<br>
+<br>
+
+## QUIZ 
+
+With the type of `append` defined as
+
+`append :: List a -> List a -> List a`
+
+what would be result of
+
+```haskell
+append (Cons 'a' (Cons 'b' Nil)) (Cons True Nil)
 ```
 
+**A.** `Cons 'a' (Cons 'b' (Cons True Nil))`
+
+**B.** `Cons 'a' (Cons 'b' Nil)`
+
+**C.** Type error
+
+(I) final    
+
+    *Answer:* C
+
 <br>
 <br>
 <br>