a-a a-b a-c aaa aab aac aak aan aao aar ab- aba abb abc abk abn abo abr ac- aca acb acc ack acn aco acr aka akb akc akk akn ako akr an- ana anb anc ank ann ano anr aoa aob aoc aok aon aoo aor ar- ara arb arc ark arn aro arr baa bab bac bak ban bao bar bba bbb bbc bbk bbn bbo bbr bca bcb bcc bck bcn bco bcr bka bkb bkc bkk bkn bko bkr bna bnb bnc bnk bnn bno bnr boa bob boc bok bon boo bor bra brb brk brn bro brr c-- caa cab cac cak can cao car cba cbb cbc cbk cbn cbo cbr cca ccb ccc cck ccn cco ccr cka ckb ckc cko cn- cna cnb cnc cnn cno cnr co- coa cob coc cok con coo cor cra crb crc crk crn cro crr ka- kaa kab kac kak kan kao kar kba kbb kbc kbk kbn kbo kbr kca kcb kcc kck kcn kcr kkb kkc kkk kkn kkr kn- kna knc knk knn kno knr koa kob koc kok kon koo kor kra krc krk krn kro krr naa nab nac nak nan nao nar nba nbb nbc nbk nbn nbo nbr nca ncb ncc nck ncn nco ncr nka nkc nkk nkn nko nkr nna nnb nnc nnk nnn nno no- noa nob noc nok non noo nor nra nrb nrc nrk nrn nro nrr oaa oab oac oak oan oao oar ob- oba obb obc obk obn obo obr oc- oca ocb occ ock ocn oco ocr oka okb okc okk oko okr on- ona onb onc onk onn ono onr oo- ooa oob ooc ook oon ooo oor or- ora orb orc ork orn oro orr ra- raa rab rac rak ran rao rar rba rbb rbc rbk rbn rbo rbr rca rcb rcc rcn rco rcr rkb rkc rkk rko rna rnb rnc rnn rno rnr roa rob roc rok ron roo ror rra rrb rrc rrk rrn rrr