diff --git a/lib/linguist/samples.json b/lib/linguist/samples.json
index 273c5360..81464828 100644
--- a/lib/linguist/samples.json
+++ b/lib/linguist/samples.json
@@ -848,8 +848,8 @@
       "exception.zep.php"
     ]
   },
-  "tokens_total": 659103,
-  "languages_total": 903,
+  "tokens_total": 659134,
+  "languages_total": 904,
   "tokens": {
     "ABAP": {
       "*/**": 1,
@@ -55927,15 +55927,15 @@
       "TWO_PI": 1
     },
     "Prolog": {
-      "-": 348,
+      "-": 350,
       "module": 4,
-      "(": 1156,
+      "(": 1161,
       "cpa_admin": 1,
       "[": 290,
       "change_password_form//1": 1,
       "]": 288,
-      ")": 1153,
-      ".": 230,
+      ")": 1158,
+      ".": 232,
       "use_module": 20,
       "user": 45,
       "user_db": 1,
@@ -55973,7 +55973,7 @@
       "user_logout": 4,
       "settings": 4,
       "save_settings": 3,
-      "%": 193,
+      "%": 194,
       "+": 47,
       "Request": 46,
       "HTTP": 4,
@@ -56326,6 +56326,13 @@
       "save": 1,
       "with": 3,
       "br": 1,
+      "subset": 2,
+      "Set": 4,
+      "Subset": 6,
+      "append": 3,
+      "L1": 1,
+      "powerset": 1,
+      "bagof": 1,
       "format_spec": 12,
       "format_error/2": 1,
       "format_spec/2": 1,
@@ -56562,7 +56569,6 @@
       "Goals": 2,
       "Tmp": 3,
       "instantiation_error": 1,
-      "append": 2,
       "NewArgs": 2,
       "variant_sha1": 1,
       "Sha": 2,
@@ -73110,7 +73116,7 @@
     "PostScript": 107,
     "PowerShell": 12,
     "Processing": 74,
-    "Prolog": 6885,
+    "Prolog": 6916,
     "Propeller Spin": 13519,
     "Protocol Buffer": 63,
     "PureScript": 1652,
@@ -73324,7 +73330,7 @@
     "PostScript": 1,
     "PowerShell": 2,
     "Processing": 1,
-    "Prolog": 6,
+    "Prolog": 7,
     "Propeller Spin": 10,
     "Protocol Buffer": 1,
     "PureScript": 4,
@@ -73391,5 +73397,5 @@
     "fish": 3,
     "wisp": 1
   },
-  "md5": "1500ca2d5506e7d4e02f8c1d14e348a4"
+  "md5": "50b2227d023291a6a909ca3866c171c8"
 }
\ No newline at end of file
diff --git a/samples/Prolog/ex6.pl b/samples/Prolog/ex6.pl
new file mode 100644
index 00000000..0b1b74eb
--- /dev/null
+++ b/samples/Prolog/ex6.pl
@@ -0,0 +1,5 @@
+%6.8
+subset(Set, Subset) :-
+	append(L1, Subset, Set).
+powerset(Set, Subset) :-
+	bagof(Subset, subset(Set, Subset), Subset).