a-a a-b aaa aab aak aan aar aax ab- aba abb abk abn abr abx aka akb akk akn akr an- ana anb ank ann anr anx ar- ara arb ark arn arr arx ax- axa axk axn axr axx baa bab bak ban bar bax bba bbb bbk bbn bbr bbx bka bkb bkk bkn bkr bkx bna bnb bnk bnn bnr bnx bra brb brk brn brr brx bxb bxn bxx ka- kaa kab kak kan kar kax kba kbb kbk kbn kbr kbx kkb kkk kkn kkr kn- kna knk knn knr knx kra krk krn krr naa nab nak nan nar nax nba nbb nbk nbn nbr nbx nka nkk nkn nkr nna nnb nnk nnn nra nrb nrk nrn nrr nrx ra- raa rab rak ran rar rax rba rbb rbk rbn rbr rbx rkb rkk rna rnb rnn rnr rra rrb rrk rrn rrr rxr xaa xak xan xar xbr xbx xkb xna xnk xrx xxx