bbb bbk bbn bbo bbr bkb bkk bkn bko bkr bnb bnk bnn bno bnr bob bok bon boo bor brb brk brn bro brr kbb kbk kbn kbo kbr kkb kkk kkn kkr kn- knk knn kno knr kob kok kon koo kor krk krn kro krr nbb nbk nbn nbo nbr nkk nkn nko nkr nnb nnk nnn nno no- nob nok non noo nor nrb nrk nrn nro nrr ob- obb obk obn obo obr okb okk oko okr on- onb onk onn ono onr oo- oob ook oon ooo oor or- orb ork orn oro orr rbb rbk rbn rbo rbr rkb rkk rko rnb rnn rno rnr rob rok ron roo ror rrb rrk rrn rrr