a-a a-b a-t aaa aab aak aao aar aat ab- aba abb abk abo abr abt aka akb akk ako akr aoa aob aok aoo aor aot ar- ara arb ark aro arr art at- ata atb ato atr att baa bab bak bao bar bat bba bbb bbk bbo bbr bbt bka bkb bkk bko bkr bkt boa bob bok boo bor bot bra brb brk bro brr brt bta btb btk bto btr btt k-t ka- kaa kab kak kao kar kat kba kbb kbk kbo kbr kkb kkk kkr kkt koa kob kok koo kor kot kra krk kro krr krt kta ktb ktk kto ktr ktt oaa oab oak oao oar oat ob- oba obb obk obo obr obt oka okb okk oko okr oo- ooa oob ook ooo oor oot or- ora orb ork oro orr ort ot- ota otb otk oto otr ott ra- raa rab rak rao rar rat rba rbb rbk rbo rbr rbt rkb rkk rko rkt roa rob rok roo ror rot rra rrb rrk rrr rrt rta rtb rtk rto rtr rtt taa tab tak tao tar tat tba tbb tbk tbo tbr tbt tka tkb tkk tko tkr tkt to- toa tob tok too tor tot tra trb trk tro trr trt tta ttb ttk tto ttr ttt