bbbb bblb blbt blub blur blut bnrr brrr brun brut btrt bttb bubb bubu bulb bull bult bulu bunb bunn bunt bunu bur- burb burl burn burr burt buru but- butt lblr lbrt llll lrrr ltbl ltnt lttr lull lulu lunn lunt lurt nlrb nnnn nntn nrlb nrrl nrtl ntnu ntrl ntru nttr nubl null nunn nunt nurl nurn nurr nurt nuru nutt nutu rbbb rbbr rnbr rnnt rnut rrrr rrun rtlt rubb rubu rull runn runt ruru rutl rutt rutu ruun tbrb tnut trtr trub trun trut truu ttbb tttt ttul tubb tubr tubu tull tulu tunb tunn tunu turb turn turr turt turu tutl tutt tutu ullr ultt ulul untb unut urun urur urut uttu uulu uuuu