a-a a-b a-c aaa aab aac aaf aan aao ab- aba abb abc abf abn abo ac- aca acb acc acf acn aco af- afa afb afc aff afn afo an- ana anb anc anf ann ano aoa aob aoc aof aon aoo baa bab bac baf ban bao bba bbb bbc bbf bbn bbo bca bcb bcc bcf bcn bco bfa bfb bfc bff bfn bfo bna bnb bnc bnf bnn bno boa bob boc bof bon boo c-- caa cab cac caf can cao cba cbb cbc cbf cbn cbo cca ccb ccc ccf ccn cco cfa cfb cfc cff cfn cfo cn- cna cnb cnc cnf cnn cno co- coa cob coc cof con coo faa fab fac faf fan fao fba fbb fbc fbf fbn fbo fca fcb fcc fcf fcn fco ffa ffc fff ffn ffo fna fnb fnc fnf fnn foa fob foc fof fon foo naa nab nac naf nan nao nba nbb nbc nbf nbn nbo nca ncb ncc ncf ncn nco nfa nfb nfc nff nfn nfo nna nnb nnc nnf nnn nno no- noa nob noc nof non noo oaa oab oac oaf oan oao ob- oba obb obc obf obn obo oc- oca ocb occ ocf ocn oco of- ofa ofb ofc off ofn ofo on- ona onb onc onf onn ono oo- ooa oob ooc oof oon ooo