a-a a-b a-i aaa aab aai aak aao ab- aba abb abi abk abo ai- aia aib aii aik aio aka akb aki akk ako aoa aob aoi aok aoo baa bab bai bak bao bba bbb bbi bbk bbo bi- bia bib bii bik bio bka bkb bkk bko boa bob boi bok boo ia- iaa iab iai iao iba ibb ibi ibk ibo iia iib iii iio ika ikb iki ikk iko io- ioa iob ioi ioo ka- kaa kab kai kak kao kba kbb kbi kbk kbo kia kib kii kik kio kkb kki kkk koa kob koi kok koo o-i oaa oab oai oak oao ob- oba obb obi obk obo oia oib oii oik oio oka okb oki okk oko oo- ooa oob ooi ook ooo