a-a a-b aaa aab aak aao aar aau ab- aba abb abk abo abr abu aka akb akk ako akr aku aoa aob aok aoo aor aou ar- ara arb ark aro arr aru au- aua aub auk auo aur b-u baa bab bak bao bar bau bba bbb bbk bbo bbr bbu bka bkb bkk bko bkr boa bob bok boo bor bou bra brb brk bro brr bru bua bub buk buo bur buu ka- kaa kab kak kao kar kau kba kbb kbk kbo kbr kbu kkb kkk kkr kku koa kob kok koo kor kou kra krk kro krr kru kub kuk kur kuu oaa oab oak oao oar oau ob- oba obb obk obo obr obu oka okb okk oko okr oku oo- ooa oob ook ooo oor or- ora orb ork oro orr oru ou- oua ouk ouo our ra- raa rab rak rao rar rau rba rbb rbk rbo rbr rbu rkb rkk rko rku roa rob rok roo ror rou rra rrb rrk rrr rru rua rub ruk ruo rur ruu ua- uaa uab uak uao uar uau uba ubb ubk ubo ubr ubu uka ukb ukk ukr uku uoa uob uok uoo uor ur- ura urb urk uro urr uru uua uur uuu