1 files changed, 60 insertions, 2 deletions
diff --git a/prolog/problems/family_relations/grandparent_2/en.py b/prolog/problems/family_relations/grandparent_2/en.py
index 3aa9bfe..b8fca7c 100644
--- a/prolog/problems/family_relations/grandparent_2/en.py
+++ b/prolog/problems/family_relations/grandparent_2/en.py
@@ -9,6 +9,64 @@ description = '''\
   X = patricia.
 ?- grandparent(tina, vanessa).
   true.
-</pre>'''
+</pre>
+<p><a target="_blank" href="[%@resource famrel.svg%]">Family trees</a> are
+described with predicates <code>parent/2</code>, <code>male/1</code>, and
+<code>female/1</code>.</p>
+'''
 
-hint = {}
+plan = ['''\
+<p><img src="[%@resource Prolog_grandparent_01.svg%]" alt="A grandparent has a child that has a child." /></p>
+''', '''\
+<p>If <code>X</code> is a parent of a parent of <code>Y</code>,
+then <code>X</code> is a grandparent of <code>Y</code>.</p>
+''', '''\
+<p><img src="[%@resource Prolog_grandparent_02.svg%]" alt="A grandparent has a child that has a child of
+his or her own." /></p>
+''']
+
+hint = {
+    'no_common_z': '''\
+<p>Did you connect <code>X</code> and <code>Y</code> through some common person?</p>
+''',
+
+    'gender_is_irrelevant': '''\
+<p>We're looking for a grandparent and a grandchild, the gender is not important.</p>
+''',
+
+    'gender_is_irrelevant_markup': '''\
+<p>Is this necessary?</p>
+''',
+
+    'or_instead_of_and': '''\
+<p>Did you perhaps use a semicolon (that represents logical OR) instead of a comma (logical AND)?</p>
+''',
+
+    'x_must_be_parent': '''\
+<p>A grandparent surely has a child, right? So he or she is a parent of someone...</p>
+<p><img src="[%@resource Prolog_grandparent_03.svg%]" </p>
+''',
+
+    'x_need_not_have_parent': '''\
+<p>A parent of <code>X</code> is not really important if we're looking for a grandchild...</p>
+''',
+
+    'y_must_have_parent': '''\
+<p>A grandchild <code>Y</code> must have a parent, right? And that parent is...</p>
+<p><img src="[%@resource Prolog_grandparent_04.svg%]" </p>
+''',
+
+    'y_need_not_be_parent': '''\
+<p>A grandchild <code>Y</code> doesn't really need to have children...</p>
+''',
+
+    'predicate_always_false': '''\
+<p>It seems your predicate is <em>always</em> "false". Did you give it the correct name,
+or is it perhaps misspelled?</p>
+<p>If the name is correct, check whether something else is misspelled, perhaps there is a full stop instead of
+a comma or vice versa, or maybe you typed a variable name in lowercase?</p>
+<p>It is, of course, also possible that your conditions are too restrictive, or even impossible to satisfy
+(as would be, for example, the condition that <code>X</code> is both a parent and a sister of <code>Y</code>, or
+something similarly impossible).</p>
+''',
+}