2 files changed, 27 insertions, 0 deletions
diff --git a/prolog/problems/denotational_semantics/prog_listswap_2/common.py b/prolog/problems/denotational_semantics/prog_listswap_2/common.py
new file mode 100644
index 0000000..ae1c220
--- /dev/null
+++ b/prolog/problems/denotational_semantics/prog_listswap_2/common.py
@@ -0,0 +1,16 @@
+id = 175
+group = 'denotational_semantics'
+number = 79
+visible = True
+facts = None
+
+solution = '''\
+program --> [begin], instructs175, [end].
+
+instructs175 --> instr175.
+instructs175 --> instr175, instructs175.
+
+instr175 --> [left].
+instr175 --> [right].
+instr175 --> [swap].
+'''
diff --git a/prolog/problems/denotational_semantics/prog_listswap_2/en.py b/prolog/problems/denotational_semantics/prog_listswap_2/en.py
new file mode 100644
index 0000000..4dd0ed5
--- /dev/null
+++ b/prolog/problems/denotational_semantics/prog_listswap_2/en.py
@@ -0,0 +1,11 @@
+id = 175
+name = 'prog_listswap/2'
+slug = 'list-manipulation language'
+
+description = '''\
+<p>Write a DCG for manipulating list elements. The first symbol in every word is <code>[begin]</code>, followed by any sequence of "instruction" symbols from the set {<code>left</code>, <code>right</code>, <code>swap</code>}, and finally <code>[end]</code>. The starting symbol should be named <code>prog_listswap</code>.</p>
+
+<p>Example words: <code>[begin,right,swap,end]</code>, <code>[begin,right,left,end]</code>.</p>
+'''
+
+hint = {}