bbbb bbbs bblb bbls blbt blls blss blst blts blub blur blus blut brls brrr brrs brsb brsr brst brus brut bsts btrt btss bttb btus bubb bubs bubu bulb bull buls bult bulu bur- burb burl burr burs burt buru buss bust busu but- buts butt buus lblr lbrs lbrt llbs llll lrrr lrst lrts ls-r lsbu lssr lsts ltbl ltrs ltsr lttr lubs lull lulu lurs lurt luss lust luts rbbb rbbr rbbs rbsl rbss rbst rlls rrrr rssl rsts rstu rtls rtlt rtss rtts rubb rubs rubu rull rurs ruru russ rust rusu rutl ruts rutt rutu sbbs sbst sbus slrs slst slsu slts slub slur slut srtr srub ssbr sslt ssrl ssrs sssb ssss sstb sstl ssts stbs stlt strs stru stss sttr stub stul stur stus stut sub- subb subl subs sul- sull sult sulu sur- surr surs surt suru sus- suss sust susu sutu suus tbbs tbrb tbst tlrs trst trtr trub trus trut truu tssr tsst tsts ttbb ttss tttt ttul tubb tubr tubs tubu tull tulu turb turr turs turt turu tuss tust tutl tuts tutt tutu ubls ullr ults ultt ulul ulus urbs urls urss ursu urts urur urus urut usbl usbr usbs uslu ussb ussr usss usst ussu ustb usts usul usus utsl uttu uulu uuuu