a-a a-b a-c aaa aab aac aaf aan ab- aba abb abc abf abn ac- aca acb acc acf acn af- afa afb afc aff afn an- ana anb anc anf ann baa bab bac baf ban bba bbb bbc bbf bbn bca bcb bcc bcf bcn bfa bfb bfc bff bfn bna bnb bnc bnf bnn c-- caa cab cac caf can cba cbb cbc cbf cbn cca ccb ccc ccf ccn cfa cfb cfc cff cfn cn- cna cnb cnc cnf cnn faa fab fac faf fan fba fbb fbc fbf fbn fca fcb fcc fcf fcn ffa ffc fff ffn fna fnb fnc fnf fnn naa nab nac naf nan nba nbb nbc nbf nbn nca ncb ncc ncf ncn nfa nfb nfc nff nfn nna nnb nnc nnf nnn