a-a a-b aaa aab aak aan aar ab- aba abb abk abn abr aka akb akk akn akr an- ana anb ank ann anr ar- ara arb ark arn arr baa bab bak ban bar bba bbb bbk bbn bbr bka bkb bkk bkn bkr bna bnb bnk bnn bnr bra brb brk brn brr ka- kaa kab kak kan kar kba kbb kbk kbn kbr kkb kkk kkn kkr kn- kna knk knn knr kra krk krn krr naa nab nak nan nar nba nbb nbk nbn nbr nka nkk nkn nkr nna nnb nnk nnn nra nrb nrk nrn nrr ra- raa rab rak ran rar rba rbb rbk rbn rbr rkb rkk rna rnb rnn rnr rra rrb rrk rrn rrr