a-a a-b aaa aab aaf aan aao aar ab- aba abb abf abn abo abr af- afa afb aff afn afo afr an- ana anb anf ann ano anr aoa aob aof aon aoo aor ar- ara arb arf arn aro arr baa bab baf ban bao bar bba bbb bbf bbn bbo bbr bfa bfb bff bfn bfo bfr bna bnb bnf bnn bno bnr boa bob bof bon boo bor bra brb brf brn bro brr faa fab faf fan fao far fba fbb fbf fbn fbo fbr ffa fff ffn ffo ffr fna fnb fnf fnn fnr foa fob fof fon foo for fra frb frf frn fro frr naa nab naf nan nao nar nba nbb nbf nbn nbo nbr nfa nfb nff nfn nfo nfr nna nnb nnf nnn nno no- noa nob nof non noo nor nra nrb nrf nrn nro nrr oaa oab oaf oan oao oar ob- oba obb obf obn obo obr of- ofa ofb off ofn ofo ofr on- ona onb onf onn ono onr oo- ooa oob oof oon ooo oor or- ora orb orf orn oro orr ra- raa rab raf ran rao rar rba rbb rbf rbn rbo rbr rfa rfb rff rfn rfo rfr rna rnb rnn rno rnr roa rob rof ron roo ror rra rrb rrf rrn rrr