a-a a-b aaa aab aaf aam aan ab- aba abb abf abm abn af- afa afb aff afm afn ama amb amf amm amn an- ana anb anf anm ann baa bab baf bam ban bba bbb bbf bbm bbn bfa bfb bff bfm bfn bma bmb bmf bmm bmn bna bnb bnf bnn faa fab faf fam fan fba fbb fbf fbm fbn ffa fff ffm ffn fma fmb fmf fmm fmn fna fnb fnf fnm fnn m-f maa mab maf mam man mba mbb mbf mbm mfa mfb mff mfm mfn mma mmb mmf mmm mmn mna mnb mnf mnm mnn naa nab naf nam nan nba nbb nbf nbm nbn nfa nfb nff nfn nma nmb nmm nmn nna nnb nnf nnm nnn