a-a a-b a-t aaa aab aak aao aat ab- aba abb abk abo abt aka akb akk ako aoa aob aok aoo aot at- ata atb ato att baa bab bak bao bat bba bbb bbk bbo bbt bka bkb bkk bko bkt boa bob bok boo bot bta btb btk bto btt k-t ka- kaa kab kak kao kat kba kbb kbk kbo kkb kkk kkt koa kob kok koo kot kta ktb ktk kto ktt oaa oab oak oao oat ob- oba obb obk obo obt oka okb okk oko oo- ooa oob ook ooo oot ot- ota otb otk oto ott taa tab tak tao tat tba tbb tbk tbo tbt tka tkb tkk tko tkt to- toa tob tok too tot tta ttb ttk tto ttt