-er a-a a-b a-c aaa aab aac aae aak aao aap aar ab- aba abb abc abe abk abo abp abr ac- aca acb acc ace ack aco acp acr aea aeb aec aee aek aeo aep aer aka akb akc ake akk ako akp akr aoa aob aoc aoe aok aoo aop aor ap- apa apb apc ape apk apo app apr ar- ara arb arc are ark aro arp arr b-p baa bab bac bae bak bao bap bar bba bbb bbc bbe bbk bbo bbp bbr bca bcb bcc bce bck bco bcp bcr be- bea beb bec bee bek beo bep ber bka bkb bkc bke bkk bko bkp bkr boa bob boc boe bok boo bop bor bpa bpb bpc bpe bpo bpp bpr bra brb bre brk bro brp brr c-- caa cab cac cae cak cao cap car cba cbb cbc cbe cbk cbo cbp cbr cca ccb ccc cce cck cco ccp ccr ce- cea ceb cec cee cek ceo cep cer cka ckb ckc cko co- coa cob coc coe cok coo cop cor cpa cpb cpc cpe cpk cpo cpp cpr cra crb crc cre crk cro crp crr eaa eab eac eae eak eao eap ear eba ebb ebc ebe ebk ebo ebp ebr ec- eca ecb ecc ece eck eco ecr eea eeb eec eee eek eeo eep eer eka ekb ekc eke eko ekp ekr eo- eoa eob eoc eoe eok eoo eop eor ep- epa epb epc epe epo epp epr era erb erc ere erk ero erp err ka- kaa kab kac kae kak kao kap kar kba kbb kbc kbe kbk kbo kbp kbr kca kcb kcc kce kck kcp kcr ke- kea keb kec kee kek keo kep ker kkb kkc kke kkk kkp kkr koa kob koc koe kok koo kop kor kpa kpc kpe kpk kpo kpp kpr kra krc krk kro krp krr oaa oab oac oae oak oao oap oar ob- oba obb obc obe obk obo obp obr oc- oca ocb occ ock oco ocp ocr oea oeb oec oee oeo oep oer oka okb okc oke okk oko okp okr oo- ooa oob ooc ook ooo oop oor op- opa opb opc ope opk opo opp opr or- ora orb orc ore ork oro orp orr p-p paa pab pac pae pak pao pap par pba pbb pbc pbe pbk pbo pbp pbr pca pcb pcc pce pck pco pcp pcr pea peb pec pee pek peo pep per pka pkb pkc pke pko pkp pkr poa pob poc poe pok poo pop por ppa ppb ppc ppe ppk ppo ppp ppr pra prb prc pre prk pro prp prr ra- raa rab rac rae rak rao rap rar rba rbb rbc rbe rbk rbo rbp rbr rca rcb rcc rce rco rcp rcr re- rea reb rec ree rek reo rep rer rkb rkc rke rkk rko rkp roa rob roc roe rok roo rop ror rpa rpb rpc rpe rpk rpo rpp rpr rra rrb rrc rrk rrp rrr