a-a a-b a-c aaa aab aac aao aar ab- aba abb abc abo abr ac- aca acb acc aco acr aoa aob aoc aoo aor ar- ara arb arc aro arr baa bab bac bao bar bba bbb bbc bbo bbr bca bcb bcc bco bcr boa bob boc boo bor bra brb bro brr c-- caa cab cac cao car cba cbb cbc cbo cbr cca ccb ccc cco ccr co- coa cob coc coo cor cra crb crc cro crr oaa oab oac oao oar ob- oba obb obc obo obr oc- oca ocb occ oco ocr oo- ooa oob ooc ooo oor or- ora orb orc oro orr ra- raa rab rac rao rar rba rbb rbc rbo rbr rca rcb rcc rco rcr roa rob roc roo ror rra rrb rrc rrr