bbb bbk bbo bbr bkb bkk bko bkr bkv bob bok boo bor bov brb brk bro brr brv bvb bvk bvo bvr bvv kbb kbk kbo kbr kkb kkk kkr kkv kob kok koo kor krk kro krr krv kvb kvk kvo kvr kvv ob- obb obk obo obr obv okb okk oko okr oo- oob ook ooo oor oov or- orb ork oro orr orv ov- ovb ovo ovv rbb rbk rbo rbr rkb rkk rko rkv rob rok roo ror rov rrb rrk rrr rvb rvo rvr rvv vbk vbo vbr vbv vkb vob vok voo vor vov vrb vrk vrr vvb vvo vvr vvv