prd_termSeq :: TERM_SEQ -> Set.Set NAME
prd_termSeq tsec =
    case tsec of
         Term_seq t -> prd_term t
         Seq_marks s -> prd_seqmark s
prd_termSeq :: TERM_SEQ -> Set.Set NAME
prd_termSeq tsec =
    case tsec of
         Term_seq t -> prd_term t
         Seq_marks s -> prd_seqmark s
prd_termSeq tsec =
    case tsec of
         Term_seq t -> prd_term t
         Seq_marks s -> prd_seqmark s