-er a-a a-b a-c aaa aab aac aae aak aao aap aar aas ab- aba abb abc abe abk abo abp abr abs ac- aca acb acc ace ack aco acp acr acs aea aeb aec aee aek aeo aep aer aes aka akb akc ake akk ako akp akr aks aoa aob aoc aoe aok aoo aop aor aos ap- apa apb apc ape apk apo app apr aps ar- ara arb arc are ark aro arp arr ars as- asa asb asc ase ask aso asp asr ass b-p baa bab bac bae bak bao bap bar bas bba bbb bbc bbe bbk bbo bbp bbr bbs bca bcb bcc bce bck bco bcp bcr bcs be- bea beb bec bee bek beo bep ber bes bka bkb bkc bke bkk bko bkp bkr bks boa bob boc boe bok boo bop bor bos bpa bpb bpc bpe bpo bpp bpr bps bra brb bre brk bro brp brr brs bsa bsb bsc bse bsk bso bsp bsr bss c-- caa cab cac cae cak cao cap car cas cba cbb cbc cbe cbk cbo cbp cbr cbs cca ccb ccc cce cck cco ccp ccr ccs ce- cea ceb cec cee cek ceo cep cer ces cka ckb ckc cko cks co- coa cob coc coe cok coo cop cor cos cpa cpb cpc cpe cpk cpo cpp cpr cps cra crb crc cre crk cro crp crr crs csa csb csc cse csk cso csp csr css eaa eab eac eae eak eao eap ear eas eba ebb ebc ebe ebk ebo ebp ebr ebs ec- eca ecb ecc ece eck eco ecr ecs eea eeb eec eee eek eeo eep eer ees eka ekb ekc eke eko ekp ekr eks eo- eoa eob eoc eoe eok eoo eop eor eos ep- epa epb epc epe epo epp epr eps era erb erc ere erk ero erp err ers es- esa esb esc ese esk eso esp esr ess ka- kaa kab kac kae kak kao kap kar kas kba kbb kbc kbe kbk kbo kbp kbr kbs kca kcb kcc kce kck kcp kcr kcs ke- kea keb kec kee kek keo kep ker kes kkb kkc kke kkk kkp kkr kks koa kob koc koe kok koo kop kor kos kpa kpc kpe kpk kpo kpp kpr kps kra krc krk kro krp krr krs ksa ksb ksc kse ksk kso ksp ksr kss oaa oab oac oae oak oao oap oar oas ob- oba obb obc obe obk obo obp obr obs oc- oca ocb occ ock oco ocp ocr ocs oea oeb oec oee oeo oep oer oes oka okb okc oke okk oko okp okr oks oo- ooa oob ooc ook ooo oop oor oos op- opa opb opc ope opk opo opp opr ops or- ora orb orc ore ork oro orp orr ors os- osa osb osc ose osk oso osp osr oss p-p paa pab pac pae pak pao pap par pas pba pbb pbc pbe pbk pbo pbp pbr pbs pca pcb pcc pce pck pco pcp pcr pcs pea peb pec pee pek peo pep per pes pka pkb pkc pke pko pkp pkr pks poa pob poc poe pok poo pop por pos ppa ppb ppc ppe ppk ppo ppp ppr pps pra prb prc pre prk pro prp prr prs ps- psa psb psc pse psk pso psp psr pss ra- raa rab rac rae rak rao rap rar ras rba rbb rbc rbe rbk rbo rbp rbr rbs rca rcb rcc rce rco rcp rcr rcs re- rea reb rec ree rek reo rep rer res rkb rkc rke rkk rko rkp rks roa rob roc roe rok roo rop ror ros rpa rpb rpc rpe rpk rpo rpp rpr rps rra rrb rrc rrk rrp rrr rrs rsa rsb rsc rse rsk rso rsp rsr rss saa sab sac sae sak sao sap sar sas sba sbb sbc sbe sbk sbo sbp sbr sbs sca scb scc sce sck sco scp scr scs se- sea seb sec see sek seo sep ser ses sk- ska skb skc ske skk sko skp skr sks soa sob soc soe sok soo sop sor sos spa spb spc spe spk spo spp spr sps sr- sra srb src sre srk sro srp srr srs ss- ssa ssb ssc sse ssk sso ssp ssr sss