a-a a-b a-c aaa aab aac aan aao aar ab- aba abb abc abn abo abr ac- aca acb acc acn aco acr an- ana anb anc ann ano anr aoa aob aoc aon aoo aor ar- ara arb arc arn aro arr baa bab bac ban bao bar bba bbb bbc bbn bbo bbr bca bcb bcc bcn bco bcr bna bnb bnc bnn bno bnr boa bob boc bon boo bor bra brb brn bro brr c-- caa cab cac can cao car cba cbb cbc cbn cbo cbr cca ccb ccc ccn cco ccr cn- cna cnb cnc cnn cno cnr co- coa cob coc con coo cor cra crb crc crn cro crr naa nab nac nan nao nar nba nbb nbc nbn nbo nbr nca ncb ncc ncn nco ncr nna nnb nnc nnn nno no- noa nob noc non noo nor nra nrb nrc nrn nro nrr oaa oab oac oan oao oar ob- oba obb obc obn obo obr oc- oca ocb occ ocn oco ocr on- ona onb onc onn ono onr oo- ooa oob ooc oon ooo oor or- ora orb orc orn oro orr ra- raa rab rac ran rao rar rba rbb rbc rbn rbo rbr rca rcb rcc rcn rco rcr rna rnb rnc rnn rno rnr roa rob roc ron roo ror rra rrb rrc rrn rrr