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diff --git a/prolog/problems/sets/union_3/en.py b/prolog/problems/sets/union_3/en.py
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+++ b/prolog/problems/sets/union_3/en.py
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+id = 128
+name = 'union/3'
+slug = 'find the union of two sets'
+
+description = '''\
+<p><code>union(S1, S2, U)</code>: the list <code>U</code> contains all elements of <code>S1</code> and <code>S2</code>, with no duplicates.</p>
+<pre>
+  ?- union([1,5,2,3], [3,4,8,2], U).
+    U = [1,5,3,4,8,2].
+</pre>'''
+
+hint = {}