a-a a-b aaa aab aak aao aay ab- aba abb abk abo aby aka akb akk ako aoa aob aok aoo ay- aya ayk ayo baa bab bak bao bay bba bbb bbk bbo bby bka bkb bkk bko boa bob bok boo boy by- bya byk byo ka- kaa kab kak kao kay kba kbb kbk kbo kkb kkk kky koa kob kok koo koy kya kyo oaa oab oak oao ob- oba obb obk obo oby oka okb okk oko oo- ooa oob ook ooo oya oyo yaa yab yak yao yay yby yka ykk yob yok yoo yoy yyb yyy