-er a-a a-b a-c aaa aab aac aae aao aar aas ab- aba abb abc abe abo abr abs ac- aca acb acc ace aco acr acs aea aeb aec aee aeo aer aes aoa aob aoc aoe aoo aor aos ar- ara arb arc are aro arr ars as- asa asb asc ase aso asr ass baa bab bac bae bao bar bas bba bbb bbc bbe bbo bbr bbs bca bcb bcc bce bco bcr bcs be- bea beb bec bee beo ber bes boa bob boc boe boo bor bos bra brb bre bro brr brs bsa bsb bsc bse bso bsr bss c-- caa cab cac cae cao car cas cba cbb cbc cbe cbo cbr cbs cca ccb ccc cce cco ccr ccs ce- cea ceb cec cee ceo cer ces co- coa cob coc coe coo cor cos cra crb crc cre cro crr crs csa csb csc cse cso csr css eaa eab eac eae eao ear eas eba ebb ebc ebe ebo ebr ebs ec- eca ecb ecc ece eco ecr ecs eea eeb eec eee eeo eer ees eo- eoa eob eoc eoe eoo eor eos era erb erc ere ero err ers es- esa esb esc ese eso esr ess oaa oab oac oae oao oar oas ob- oba obb obc obe obo obr obs oc- oca ocb occ oco ocr ocs oea oeb oec oee oeo oer oes oo- ooa oob ooc ooo oor oos or- ora orb orc ore oro orr ors os- osa osb osc ose oso osr oss ra- raa rab rac rae rao rar ras rba rbb rbc rbe rbo rbr rbs rca rcb rcc rce rco rcr rcs re- rea reb rec ree reo rer res roa rob roc roe roo ror ros rra rrb rrc rrr rrs rsa rsb rsc rse rso rsr rss saa sab sac sae sao sar sas sba sbb sbc sbe sbo sbr sbs sca scb scc sce sco scr scs se- sea seb sec see seo ser ses soa sob soc soe soo sor sos sr- sra srb src sre sro srr srs ss- ssa ssb ssc sse sso ssr sss