bbbb bbbs bblb bbls blbt blls blss blst blts blub blus blut bsts btss bttb btus bubb bubs bubu bulb bull buls bult bulu buss bust busu but- buts butt buus llbs llll lsbu lsts ltbl lubs lull lulu luss lust luts sbbs sbst sbus slst slsu slts slub slut sslt sssb ssss sstb sstl ssts stbs stlt stss stub stul stus stut sub- subb subl subs sul- sull sult sulu sus- suss sust susu sutu suus tbbs tbst tsst tsts ttbb ttss tttt ttul tubb tubs tubu tull tulu tuss tust tutl tuts tutt tutu ubls ults ultt ulul ulus usbl usbs uslu ussb usss usst ussu ustb usts usul usus utsl uttu uulu uuuu