prd_sentence :: SENTENCE -> Set.Set NAME
prd_sentence s =
    case s of
         Quant_sent q _ -> prd_quantSent q
         Bool_sent b _ -> prd_boolSent b
         Atom_sent a _ -> prd_atomSent a
         Comment_sent _ c _ -> prd_sentence c
         Irregular_sent i _ -> prd_sentence i
prd_sentence :: SENTENCE -> Set.Set NAME
prd_sentence s =
    case s of
         Quant_sent q _ -> prd_quantSent q
         Bool_sent b _ -> prd_boolSent b
         Atom_sent a _ -> prd_atomSent a
         Comment_sent _ c _ -> prd_sentence c
         Irregular_sent i _ -> prd_sentence i
prd_sentence s =
    case s of
         Quant_sent q _ -> prd_quantSent q
         Bool_sent b _ -> prd_boolSent b
         Atom_sent a _ -> prd_atomSent a
         Comment_sent _ c _ -> prd_sentence c
         Irregular_sent i _ -> prd_sentence i