a-a a-b aaa aab aaf aak aau ab- aba abb abf abk abu af- afa afb aff afk afu aka akb akk aku au- aua aub auf auk b-u baa bab baf bak bau bba bbb bbf bbk bbu bfa bfb bff bfu bka bkb bkf bkk bua bub buf buk buu faa fab faf fak fau fba fbb fbf fbk fbu ffa fff ffk ffu fka fkb fkf fkk fua fub fuf fuk fuu ka- kaa kab kaf kak kau kba kbb kbf kbk kbu kfa kff kfu kkb kkk kku kub kuk kuu ua- uaa uab uaf uak uau uba ubb ubf ubk ubu ufa uff ufu uka ukb ukf ukk uku uua uuu