1 files changed, 83 insertions, 3 deletions
diff --git a/prolog/problems/family_relations/ancestor_2/en.py b/prolog/problems/family_relations/ancestor_2/en.py
index 5ae1bd0..cec2a29 100644
--- a/prolog/problems/family_relations/ancestor_2/en.py
+++ b/prolog/problems/family_relations/ancestor_2/en.py
@@ -2,12 +2,92 @@ name = 'ancestor/2'
 slug = 'the ancestor relation'
 
 description = '''\
-<p><code>ancestor(X, Y)</code>: <code>X</code> is an ancestor (parent, grandparent, …) of <code>Y</code>.</p>
+<p><code>ancestor(X, Y)</code>: <code>X</code> is an ancestor (parent, grandparent, grandgrandparent, ...) of <code>Y</code>.</p>
 <pre>
 ?- ancestor(patricia, X).
   X = john ;
   X = michael ;
   X = michelle.
-</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>
+'''
+
+plan = ['''\
+<p>It's time to use recursion for the first time... how can we transpose the problem to a smaller one (a single step smaller that is)?</p>
+<p><img src="[%@resource Prolog_ancestor_03.svg%]" alt="A parent of someone, who is a parent of Y, is also an ancestor of Y." /></p>
+''', '''\
+<p>If <code>X</code> is a parent of some <code>Z</code> and that <code>Z</code> is an ancestor of <code>Y</code>,
+then <code>X</code> is also an ancestor of <code>Y</code>.</p>
+''', '''\
+<p><img src="[%@resource Prolog_ancestor_04.svg%]" alt="If X is a parent of Z, and Z is an ancestor of Y, then X is also an ancestor of Y." /></p>
+''']
+
+hint = {
+    'gender_is_irrelevant': '''\
+<p>Is gender really important?</p>
+''',
+
+    'gender_is_irrelevant_markup': '''\
+<p>Is this necessary?</p>
+''',
+
+    'grandparent_used': '''\
+<p>The solution using the grandparent relation will not be general enough, try using recursion instead.
+Try to transpose the problem into a "smaller" one, e.g. an ancestor in one step less (a closer ancestor).</p>
+''',
+
+    'grandparent_used_markup': '''\
+<p>Can you solve without using this?</p>
+''',
+
+    'base_case': '''\
+<p>Did you think of a base case? The recursion has to stop at some point.
+What is the most obvious pair (ancestor, descendand)?</p>
+<p><img src="[%@resource Prolog_ancestor_01.svg%]" /></p>
+''',    # TODO: morda ta hint naredim z "more": najprej tekst, ob kliku pa še slika... (sicer je preveč očitno)
+
+    'ancestor_to_oneself': '''\
+<p>How can anyone be an ancestor to him- or herself? This can be inferred from the current version of the program.
+It might also help to graphically sketch your current solution.</p>
+''',
+
+    'ancestor_to_oneself_with_or': '''\
+<p>How can anyone be an ancestor to him- or herself? This can be inferred from the current version of the program.
+It might help to graphically sketch your current solution.</p>
+<p>Perhaps you should also check your use of the semicolon. The semicolon basically creates two separate clauses or
+branches (one or the other can hold, or even both). However, be careful, as this two branches are independent of
+one another -- assigned values to variables in one branch do not transfer to the other branch.</p>
+''',
+
+    'only_two_levels_deep': '''\
+<p>Your solution is not general enough. An ancestor can also be someone "more steps away" than grandparents,
+e.g. grandgrandparents or grandgrandgrandparents are also ancestors.</p>
+''',
+
+    'descendant_need_not_be_parent': '''\
+<p>The descendant <code>Y</code> doesn't actually need to have any children...</p>
+''',
+
+    'wrong_direction': '''\
+<p>Did you perhaps program exactly the reverse relation, descendant instead of ancestor?
+<code>X</code> should be an ancestor of <code>Y</code> and not the other way around!</p>
+<p><img src="[%@resource Prolog_ancestor_02.svg%]" /></p>
+''',
+
+    'predicate_always_false': '''\
+<p>It seems your predicate is <emph>always</emph> "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 parent and a sister of <code>Y</code>, or
+something similar).</p>
+''',
+
+    'timeout': '''\
+<p>Is there an infinite recursion at work here? How will it ever stop?</p>
+<p>Or perhaps is there a missing, faulty, or simply incompatible (with the general recursive case) base case?</p>
+''',
+}
 
-hint = {}