Using trie more.

src/GF/Canon/CMacros.hs

@@ -161,7 +161,7 @@ wordsInTerm trm = filter (not . null) $ case trm of
    T _ cs  -> concat [wo t | Cas _ t <- cs]
    C s t   -> wo s ++ wo t
    FV ts   -> concatMap wo ts
-   K (KP ss vs) -> ss ++ concat [s ++ t | Var s t <- vs]
+   K (KP ss vs) -> ss ++ concat [s | Var s _ <- vs]
    P t _   -> wo t --- not needed ?
    _       -> []
  where wo = wordsInTerm

src/GF/Canon/Look.hs

@@ -166,4 +166,7 @@ ccompute cnc = comp []
      noVar v = case v of
        LI _ -> False
        R rs -> all noVar [t | Ass _ t <- rs]
-       _    -> True --- other cases?
+       Con _ ts -> all noVar ts
+       FV ts -> all noVar ts
+       S x y -> noVar x && noVar y
+       _    -> True --- other cases that can be values to pattern match?