a-a a-b aaa aab aak aao aar aay ab- aba abb abk abo abr aby aka akb akk ako akr aoa aob aok aoo aor ar- ara arb ark aro arr ary ay- aya ayk ayo ayr baa bab bak bao bar bay bba bbb bbk bbo bbr bby bka bkb bkk bko bkr boa bob bok boo bor boy bra brb brk bro brr bry by- bya byk byo byr ka- kaa kab kak kao kar kay kba kbb kbk kbo kbr kkb kkk kkr kky koa kob kok koo kor koy kra krk kro krr kry kya kyo kyr oaa oab oak oao oar ob- oba obb obk obo obr oby oka okb okk oko okr oo- ooa oob ook ooo oor or- ora orb ork oro orr ory oya oyo ra- raa rab rak rao rar ray rba rbb rbk rbo rbr rkb rkk rko rky roa rob rok roo ror roy rra rrb rrk rrr ry- rya ryk ryo ryr ryy yaa yab yak yao yar yay ybr yby yka ykk yob yok yoo yor yoy yra yro yyb yyy