a-a a-b aaa aab aam aan aao ab- aba abb abm abn abo ama amb amm amn amo an- ana anb anm ann ano aoa aob aom aon aoo baa bab bam ban bao bba bbb bbm bbn bbo bma bmb bmm bmn bmo bna bnb bnn bno boa bob bom bon boo m-o maa mab mam man mao mba mbb mbm mbo mma mmb mmm mmn mmo mna mnb mnm mnn mno moa mob mom mon moo naa nab nam nan nao nba nbb nbm nbn nbo nma nmb nmm nmn nmo nna nnb nnm nnn nno no- noa nob nom non noo oaa oab oam oan oao ob- oba obb obm obn obo om- oma omb omm omn omo on- ona onb onn ono oo- ooa oob oom oon ooo