a-a a-b a-i aaa aab aai aak aao aas ab- aba abb abi abk abo abs ai- aia aib aii aik aio ais aka akb aki akk ako aks aoa aob aoi aok aoo aos as- asa asb asi ask aso ass baa bab bai bak bao bas bba bbb bbi bbk bbo bbs bi- bia bib bii bik bio bis bka bkb bkk bko bks boa bob boi bok boo bos bsa bsb bsi bsk bso bss ia- iaa iab iai iao ias iba ibb ibi ibk ibo ibs iia iib iii iio iis ika ikb iki ikk iko iks io- ioa iob ioi ioo ios is- isa isb isi isk iso iss ka- kaa kab kai kak kao kas kba kbb kbi kbk kbo kbs kia kib kii kik kio kis kkb kki kkk kks koa kob koi kok koo kos ksa ksb ksi ksk kso kss o-i oaa oab oai oak oao oas ob- oba obb obi obk obo obs oia oib oii oik oio ois oka okb oki okk oko oks oo- ooa oob ooi ook ooo oos os- osa osb osi osk oso oss saa sab sai sak sao sas sba sbb sbi sbk sbo sbs sia sib sii sik sio sis sk- ska skb ski skk sko sks soa sob soi sok soo sos ss- ssa ssb ssi ssk sso sss