-er a-a a-b aaa aab aae aak aan aar aas ab- aba abb abe abk abn abr abs aea aeb aee aek aen aer aes aka akb ake akk akn akr aks an- ana anb ane ank ann anr ans ar- ara arb are ark arn arr ars as- asa asb ase ask asn asr ass baa bab bae bak ban bar bas bba bbb bbe bbk bbn bbr bbs be- bea beb bee bek ben ber bes bka bkb bke bkk bkn bkr bks bna bnb bne bnk bnn bnr bns bra brb bre brk brn brr brs bsa bsb bse bsk bsn bsr bss eaa eab eae eak ean ear eas eba ebb ebe ebk ebn ebr ebs eea eeb eee eek een eer ees eka ekb eke ekr eks en- ena enb ene enk enn enr ens era erb ere erk ern err ers es- esa esb ese esk esn esr ess ka- kaa kab kae kak kan kar kas kba kbb kbe kbk kbn kbr kbs ke- kea keb kee kek ken ker kes kkb kke kkk kkn kkr kks kn- kna kne knk knn knr kra krk krn krr krs ksa ksb kse ksk ksn ksr kss naa nab nae nak nan nar nas nba nbb nbe nbk nbn nbr nbs ne- nea neb nee nek nen ner nes nka nke nkk nkn nkr nks nna nnb nne nnk nnn nns nra nrb nre nrk nrn nrr nrs nsa nsb nse nsk nsn nsr nss ra- raa rab rae rak ran rar ras rba rbb rbe rbk rbn rbr rbs re- rea reb ree rek ren rer res rkb rke rkk rks rna rnb rnn rnr rns rra rrb rrk rrn rrr rrs rsa rsb rse rsk rsn rsr rss saa sab sae sak san sar sas sba sbb sbe sbk sbn sbr sbs se- sea seb see sek sen ser ses sk- ska skb ske skk skr sks sna snb sne snk snn snr sns sr- sra srb sre srk srn srr srs ss- ssa ssb sse ssk ssn ssr sss