a-a a-b a-c aaa aab aac aaf aak aao aap aar ab- aba abb abc abf abk abo abp abr ac- aca acb acc acf ack aco acp acr af- afa afb afc aff afk afo afp afr aka akb akc akk ako akp akr aoa aob aoc aof aok aoo aop aor ap- apa apb apc apf apk apo app apr ar- ara arb arc arf ark aro arp arr b-p baa bab bac baf bak bao bap bar bba bbb bbc bbf bbk bbo bbp bbr bca bcb bcc bcf bck bco bcp bcr bfa bfb bfc bff bfo bfp bfr bka bkb bkc bkf bkk bko bkp bkr boa bob boc bof bok boo bop bor bpa bpb bpc bpf bpo bpp bpr bra brb brf brk bro brp brr c-- caa cab cac caf cak cao cap car cba cbb cbc cbf cbk cbo cbp cbr cca ccb ccc ccf cck cco ccp ccr cfa cfb cfc cff cfk cfo cfp cfr cka ckb ckc cko co- coa cob coc cof cok coo cop cor cpa cpb cpc cpf cpk cpo cpp cpr cra crb crc crf crk cro crp crr faa fab fac faf fak fao fap far fba fbb fbc fbf fbk fbo fbp fbr fca fcb fcc fcf fck fco fcp fcr ffa ffc fff ffk ffo ffp ffr fka fkb fkc fkf fkk fkp foa fob foc fof fok foo fop for fpa fpb fpc fpk fpo fpp fpr fra frb frc frf frk fro frp frr ka- kaa kab kac kaf kak kao kap kar kba kbb kbc kbf kbk kbo kbp kbr kca kcb kcc kck kcp kcr kfa kfc kff kfo kkb kkc kkk kkp kkr koa kob koc kof kok koo kop kor kpa kpc kpf kpk kpo kpp kpr kra krc krf krk kro krp krr oaa oab oac oaf oak oao oap oar ob- oba obb obc obf obk obo obp obr oc- oca ocb occ ocf ock oco ocp ocr of- ofa ofb ofc off ofo ofp ofr oka okb okc okk oko okp okr oo- ooa oob ooc oof ook ooo oop oor op- opa opb opc opf opk opo opp opr or- ora orb orc orf ork oro orp orr p-p paa pab pac paf pak pao pap par pba pbb pbc pbf pbk pbo pbp pbr pca pcb pcc pcf pck pco pcp pcr pfa pfb pfc pff pfk pfo pfp pfr pka pkb pkc pkf pko pkp pkr poa pob poc pof pok poo pop por ppa ppb ppc ppf ppk ppo ppp ppr pra prb prc prf prk pro prp prr ra- raa rab rac raf rak rao rap rar rba rbb rbc rbf rbk rbo rbp rbr rca rcb rcc rcf rco rcp rcr rfa rfb rfc rff rfk rfo rfp rfr rkb rkc rkf rkk rko rkp roa rob roc rof rok roo rop ror rpa rpb rpc rpf rpk rpo rpp rpr rra rrb rrc rrf rrk rrp rrr