a-a a-b aaa aab aad aaf aan aao ab- aba abb abd abf abn abo ad- ada adb add adf adn ado af- afa afb afd aff afn afo an- ana anb and anf ann ano aoa aob aod aof aon aoo baa bab bad baf ban bao bba bbb bbd bbf bbn bbo bda bdb bdd bdf bdo bfa bfb bfd bff bfn bfo bna bnb bnd bnf bnn bno boa bob bod bof bon boo daa dab dad daf dan dao dba dbb dbd dbf dbn dbo dda ddb ddd ddf ddn ddo dfa dfb dfd dff dfn dfo dna dnb dnd dnf dnn dno doa dob dod dof don doo faa fab fad faf fan fao fba fbb fbd fbf fbn fbo fda fdb fdd fdf fdn fdo ffa ffd fff ffn ffo fna fnb fnd fnf fnn foa fob fof fon foo naa nab nad naf nan nao nba nbb nbd nbf nbn nbo nda ndb ndd ndf ndn ndo nfa nfb nfd nff nfn nfo nna nnb nnf nnn nno no- noa nob nod nof non noo oaa oab oad oaf oan oao ob- oba obb obd obf obn obo oda odb odd odf odn odo of- ofa ofb ofd off ofn ofo on- ona onb ond onf onn ono oo- ooa oob ood oof oon ooo