a-a a-b a-c aaa aab aac aah aak aao ab- aba abb abc abh abk abo ac- aca acb acc ach ack aco aha ahb ahc ahh ahk aho aka akb akc akh akk ako aoa aob aoc aoh aok aoo baa bab bac bah bak bao bba bbb bbc bbh bbk bbo bca bcb bcc bch bck bco bha bhb bhc bhh bhk bho bka bkb bkc bkk bko boa bob boc boh bok boo c-- caa cab cac cah cak cao cba cbb cbc cbh cbk cbo cca ccb ccc cch cck cco ch- cha chb chc chh chk cho cka ckb ckc ckh cko co- coa cob coc coh cok coo haa hab hac hah hak hao hba hbb hbc hbh hbk hbo hca hcb hcc hch hck hco hha hhb hhc hhh hhk hho hka hkb hkh hkk hko hoa hob hoc hoh hok hoo ka- kaa kab kac kah kak kao kba kbb kbc kbh kbk kbo kca kcb kcc kch kck kha khh khk kho kkb kkc kkh kkk koa kob koc koh kok koo oaa oab oac oah oak oao ob- oba obb obc obh obk obo oc- oca ocb occ och ock oco oha ohc ohh oho oka okb okc okk oko oo- ooa oob ooc ooh ook ooo