a-a a-b a-t aaa aab aan aao aat ab- aba abb abn abo abt an- ana anb ann ano ant aoa aob aon aoo aot at- ata atb atn ato att baa bab ban bao bat bba bbb bbn bbo bbt bna bnb bnn bno bnt boa bob bon boo bot bta btb btn bto btt naa nab nan nao nat nba nbb nbn nbo nbt nna nnb nnn nno nnt no- noa nob non noo not nta ntb ntn nto ntt oaa oab oan oao oat ob- oba obb obn obo obt on- ona onb onn ono ont oo- ooa oob oon ooo oot ot- ota otb otn oto ott taa tab tan tao tat tba tbb tbn tbo tbt tna tnb tnn tno tnt to- toa tob ton too tot tta ttb ttn tto ttt