a-a a-b a-c aaa aab aac aad aak aao aar ab- aba abb abc abd abk abo abr ac- aca acb acc acd ack aco acr ad- ada adb adc add adk ado adr aka akb akc akd akk ako akr aoa aob aoc aod aok aoo aor ar- ara arb arc ard ark aro arr baa bab bac bad bak bao bar bba bbb bbc bbd bbk bbo bbr bca bcb bcc bcd bck bco bcr bda bdb bdc bdd bdk bdo bdr bka bkb bkc bkk bko bkr boa bob boc bod bok boo bor bra brb brd brk bro brr c-- caa cab cac cad cak cao car cba cbb cbc cbd cbk cbo cbr cca ccb ccc ccd cck cco ccr cda cdb cdc cdd cdk cdo cdr cka ckb ckc ckd cko co- coa cob coc cod cok coo cor cra crb crc crd crk cro crr daa dab dac dad dak dao dar dba dbb dbc dbd dbk dbo dbr dca dcb dcc dcd dck dco dcr dda ddb ddc ddd ddk ddo ddr dka dkb dkc dkk dko dkr doa dob doc dod dok doo dor dra drb drc drd drk dro drr ka- kaa kab kac kad kak kao kar kba kbb kbc kbd kbk kbo kbr kca kcb kcc kcd kck kcr kda kdb kdc kdk kdo kdr kkb kkc kkk kkr koa kob koc kod kok koo kor kra krc krd krk kro krr oaa oab oac oad oak oao oar ob- oba obb obc obd obk obo obr oc- oca ocb occ ocd ock oco ocr oda odb odc odd odo odr oka okb okc okd okk oko okr oo- ooa oob ooc ood ook ooo oor or- ora orb orc ord ork oro orr ra- raa rab rac rad rak rao rar rba rbb rbc rbd rbk rbo rbr rca rcb rcc rcd rco rcr rda rdb rdc rdd rdo rdr rkb rkc rkk rko roa rob roc rod rok roo ror rra rrb rrc rrd rrk rrr