diff --git a/examples/trigram/Trigram.gf b/examples/trigram/Trigram.gf
index 2e6e18fdd..0ad99b0bf 100644
--- a/examples/trigram/Trigram.gf
+++ b/examples/trigram/Trigram.gf
@@ -1,6 +1,9 @@
 abstract Trigram = {
 
 cat 
+    -- A sentence
+    S ;
+
     -- A lexicon is a set of 'Word's
     Word ;
 
@@ -17,6 +20,8 @@ cat
     Prob (a,b,c : Word) ;
 
 data
+    sent : ({a,b} : Word) -> Seq a b -> S ;
+
     -- Here we construct sequence by using nil and cons. The Prob argument ensures
     -- that the sequence contains only valid N-grams and contributes with the right
     -- probability mass
diff --git a/examples/trigram/TrigramCnc.gf b/examples/trigram/TrigramCnc.gf
index 917aa3db8..181750396 100644
--- a/examples/trigram/TrigramCnc.gf
+++ b/examples/trigram/TrigramCnc.gf
@@ -1,11 +1,12 @@
 concrete TrigramCnc of Trigram = {
 
 lincat 
-    Word,Seq = Str;
+    S,Word,Seq = Str;
 
     Unigram, Bigram, Trigram, Prob = {} ;
 
 lin
+    sent _ _ l = l ;
     nil  a b c _   = a ++ b ++ c ;
     cons _ _ l c _ = l ++ c ;