prd_phrase :: PHRASE -> Set.Set NAME
prd_phrase p =
    case p of
         Module m -> prd_module m
         Sentence s -> prd_sentence s
         Importation i -> prd_importation i
         Comment_text _ t _ -> prd_text t
prd_phrase :: PHRASE -> Set.Set NAME
prd_phrase p =
    case p of
         Module m -> prd_module m
         Sentence s -> prd_sentence s
         Importation i -> prd_importation i
         Comment_text _ t _ -> prd_text t
prd_phrase p =
    case p of
         Module m -> prd_module m
         Sentence s -> prd_sentence s
         Importation i -> prd_importation i
         Comment_text _ t _ -> prd_text t