a-a a-b a-c aaa aab aac aak aao aar ab- aba abb abc abk abo abr ac- aca acb acc ack aco acr aka akb akc akk ako akr aoa aob aoc aok aoo aor ar- ara arb arc ark aro arr baa bab bac bak bao bar bba bbb bbc bbk bbo bbr bca bcb bcc bck bco bcr bka bkb bkc bkk bko bkr boa bob boc bok boo bor bra brb brk bro brr c-- caa cab cac cak cao car cba cbb cbc cbk cbo cbr cca ccb ccc cck cco ccr cka ckb ckc cko co- coa cob coc cok coo cor cra crb crc crk cro crr ka- kaa kab kac kak kao kar kba kbb kbc kbk kbo kbr kca kcb kcc kck kcr kkb kkc kkk kkr koa kob koc kok koo kor kra krc krk kro krr oaa oab oac oak oao oar ob- oba obb obc obk obo obr oc- oca ocb occ ock oco ocr oka okb okc okk oko okr oo- ooa oob ooc ook ooo oor or- ora orb orc ork oro orr ra- raa rab rac rak rao rar rba rbb rbc rbk rbo rbr rca rcb rcc rco rcr rkb rkc rkk rko roa rob roc rok roo ror rra rrb rrc rrk rrr