-er a-a a-b a-c aaa aab aac aae aaf aar aas ab- aba abb abc abe abf abr abs ac- aca acb acc ace acf acr acs aea aeb aec aee aef aer aes af- afa afb afc afe aff afr afs ar- ara arb arc are arf arr ars as- asa asb asc ase asf asr ass baa bab bac bae baf bar bas bba bbb bbc bbe bbf bbr bbs bca bcb bcc bce bcf bcr bcs be- bea beb bec bee bef ber bes bfa bfb bfc bfe bff bfr bfs bra brb bre brf brr brs bsa bsb bsc bse bsf bsr bss c-- caa cab cac cae caf car cas cba cbb cbc cbe cbf cbr cbs cca ccb ccc cce ccf ccr ccs ce- cea ceb cec cee cef cer ces cfa cfb cfc cfe cff cfr cfs cra crb crc cre crf crr crs csa csb csc cse csf csr css eaa eab eac eae eaf ear eas eba ebb ebc ebe ebf ebr ebs ec- eca ecb ecc ece ecf ecr ecs eea eeb eec eee eef eer ees ef- efa efb efc efe eff efr efs era erb erc ere erf err ers es- esa esb esc ese esf esr ess faa fab fac fae faf far fas fba fbb fbc fbe fbf fbr fbs fca fcb fcc fce fcf fcr fcs fea feb fec fee fef fer fes ffa ffc ffe fff ffr ffs fra frb frc fre frf frr frs fsa fsb fsc fse fsf fsr fss ra- raa rab rac rae raf rar ras rba rbb rbc rbe rbf rbr rbs rca rcb rcc rce rcf rcr rcs re- rea reb rec ree ref rer res rfa rfb rfc rfe rff rfr rfs rra rrb rrc rrf rrr rrs rsa rsb rsc rse rsf rsr rss saa sab sac sae saf sar sas sba sbb sbc sbe sbf sbr sbs sca scb scc sce scf scr scs se- sea seb sec see sef ser ses sfa sfb sfc sfe sff sfr sfs sr- sra srb src sre srf srr srs ss- ssa ssb ssc sse ssf ssr sss