-er a-a a-b a-c aaa aab aac aae aak aar aas ab- aba abb abc abe abk abr abs ac- aca acb acc ace ack acr acs aea aeb aec aee aek aer aes aka akb akc ake akk akr aks ar- ara arb arc are ark arr ars as- asa asb asc ase ask asr ass baa bab bac bae bak bar bas bba bbb bbc bbe bbk bbr bbs bca bcb bcc bce bck bcr bcs be- bea beb bec bee bek ber bes bka bkb bkc bke bkk bkr bks bra brb bre brk brr brs bsa bsb bsc bse bsk bsr bss c-- caa cab cac cae cak car cas cba cbb cbc cbe cbk cbr cbs cca ccb ccc cce cck ccr ccs ce- cea ceb cec cee cek cer ces cka ckb ckc cks cra crb crc cre crk crr crs csa csb csc cse csk csr css eaa eab eac eae eak ear eas eba ebb ebc ebe ebk ebr ebs ec- eca ecb ecc ece eck ecr ecs eea eeb eec eee eek eer ees eka ekb ekc eke ekr eks era erb erc ere erk err ers es- esa esb esc ese esk esr ess ka- kaa kab kac kae kak kar kas kba kbb kbc kbe kbk kbr kbs kca kcb kcc kce kck kcr kcs ke- kea keb kec kee kek ker kes kkb kkc kke kkk kkr kks kra krc krk krr krs ksa ksb ksc kse ksk ksr kss ra- raa rab rac rae rak rar ras rba rbb rbc rbe rbk rbr rbs rca rcb rcc rce rcr rcs re- rea reb rec ree rek rer res rkb rkc rke rkk rks rra rrb rrc rrk rrr rrs rsa rsb rsc rse rsk rsr rss saa sab sac sae sak sar sas sba sbb sbc sbe sbk sbr sbs sca scb scc sce sck scr scs se- sea seb sec see sek ser ses sk- ska skb skc ske skk skr sks sr- sra srb src sre srk srr srs ss- ssa ssb ssc sse ssk ssr sss