bbbb bbbs bobb bobo bobs boob boor boos boot bor- boro borr bors bort boso boss bost botb boto bots bott bovo brob broo bror bros brot brrr brrs brsb brsr brst bsos bsts bstv btob btor btrt btss bttb obbo obor obos obot obro obsr obss obst obts obvs oooo ooos oort oost ootb oots orbb orbo orbs oro- oror oros orot orro orrs orso orto orts orvr orvs osoo osor osos osov osro ossb osso ostr osts otbs oto- otoo otor otos otov otro otrs otso otto otts ovo- ovoo ovot rbbb rbbr rbbs rbss rbst rob- robb robo robs robt roob roor roos root roro rort roso ross rost roto rotr rots rott rovo rovs rrrr rsos rsts rtss rtts s-os s-vt sbbs sbor sbot sbst sobo sobr sobs sobt soor soos soot sorb soro sorr sors sort soso soss sost sosv soto sots sovo sovs sros srtr srtv ssbr ssot ssrs sssb ssss sstb ssts st-v stbs stob stoo stor stos stot stro strs stss sttr stvs svor svtr tbbs tbrb tbst tobo tobs tobt toor toos toot toro torr tors tort torv tosb toso toss tost toto totr tots tott tovo troo tros trot trst trtr trvs tsob tsos tssr tsst tsts ttbb ttss tttt tvbs tvos tvro tvrr tvss tvtv voor voot vor- voro vors vort voso voss voto vrot vrto vsto vtrs vvob vvsb vvvv