a-a a-b a-c aaa aab aac aaf aak aao aas ab- aba abb abc abf abk abo abs ac- aca acb acc acf ack aco acs af- afa afb afc aff afk afo afs aka akb akc akk ako aks aoa aob aoc aof aok aoo aos as- asa asb asc asf ask aso ass baa bab bac baf bak bao bas bba bbb bbc bbf bbk bbo bbs bca bcb bcc bcf bck bco bcs bfa bfb bfc bff bfo bfs bka bkb bkc bkf bkk bko bks boa bob boc bof bok boo bos bsa bsb bsc bsf bsk bso bss c-- caa cab cac caf cak cao cas cba cbb cbc cbf cbk cbo cbs cca ccb ccc ccf cck cco ccs cfa cfb cfc cff cfk cfo cfs cka ckb ckc cko cks co- coa cob coc cof cok coo cos csa csb csc csf csk cso css faa fab fac faf fak fao fas fba fbb fbc fbf fbk fbo fbs fca fcb fcc fcf fck fco fcs ffa ffc fff ffk ffo ffs fka fkb fkc fkf fkk foa fob foc fof fok foo fos fsa fsb fsc fsf fsk fso fss ka- kaa kab kac kaf kak kao kas kba kbb kbc kbf kbk kbo kbs kca kcb kcc kck kcs kfa kfc kff kfo kfs kkb kkc kkk kks koa kob koc kof kok koo kos ksa ksb ksc ksf ksk kso kss oaa oab oac oaf oak oao oas ob- oba obb obc obf obk obo obs oc- oca ocb occ ocf ock oco ocs of- ofa ofb ofc off ofo ofs oka okb okc okk oko oks oo- ooa oob ooc oof ook ooo oos os- osa osb osc osf osk oso oss saa sab sac saf sak sao sas sba sbb sbc sbf sbk sbo sbs sca scb scc scf sck sco scs sfa sfb sfc sff sfk sfo sfs sk- ska skb skc skf skk sko sks soa sob soc sof sok soo sos ss- ssa ssb ssc ssf ssk sso sss