a-a a-b aaa aab aak aan aao aar ab- aba abb abk abn abo abr aka akb akk akn ako akr an- ana anb ank ann ano anr aoa aob aok aon aoo aor ar- ara arb ark arn aro arr baa bab bak ban bao bar bba bbb bbk bbn bbo bbr bka bkb bkk bkn bko bkr bna bnb bnk bnn bno bnr boa bob bok bon boo bor bra brb brk brn bro brr ka- kaa kab kak kan kao kar kba kbb kbk kbn kbo kbr kkb kkk kkn kkr kn- kna knk knn kno knr koa kob kok kon koo kor kra krk krn kro krr naa nab nak nan nao nar nba nbb nbk nbn nbo nbr nka nkk nkn nko nkr nna nnb nnk nnn nno no- noa nob nok non noo nor nra nrb nrk nrn nro nrr oaa oab oak oan oao oar ob- oba obb obk obn obo obr oka okb okk oko okr on- ona onb onk onn ono onr oo- ooa oob ook oon ooo oor or- ora orb ork orn oro orr ra- raa rab rak ran rao rar rba rbb rbk rbn rbo rbr rkb rkk rko rna rnb rnn rno rnr roa rob rok ron roo ror rra rrb rrk rrn rrr