a-a a-b aaa aab aan aar aas ab- aba abb abn abr abs an- ana anb ann anr ans ar- ara arb arn arr ars as- asa asb asn asr ass baa bab ban bar bas bba bbb bbn bbr bbs bna bnb bnn bnr bns bra brb brn brr brs bsa bsb bsn bsr bss naa nab nan nar nas nba nbb nbn nbr nbs nna nnb nnn nns nra nrb nrn nrr nrs nsa nsb nsn nsr nss ra- raa rab ran rar ras rba rbb rbn rbr rbs rna rnb rnn rnr rns rra rrb rrn rrr rrs rsa rsb rsn rsr rss saa sab san sar sas sba sbb sbn sbr sbs sna snb snn snr sns sr- sra srb srn srr srs ss- ssa ssb ssn ssr sss