-er a-a a-b a-c aaa aab aac aae aaf aao aar ab- aba abb abc abe abf abo abr ac- aca acb acc ace acf aco acr aea aeb aec aee aef aeo aer af- afa afb afc afe aff afo afr aoa aob aoc aoe aof aoo aor ar- ara arb arc are arf aro arr baa bab bac bae baf bao bar bba bbb bbc bbe bbf bbo bbr bca bcb bcc bce bcf bco bcr be- bea beb bec bee bef beo ber bfa bfb bfc bfe bff bfo bfr boa bob boc boe bof boo bor bra brb bre brf bro brr c-- caa cab cac cae caf cao car cba cbb cbc cbe cbf cbo cbr cca ccb ccc cce ccf cco ccr ce- cea ceb cec cee cef ceo cer cfa cfb cfc cfe cff cfo cfr co- coa cob coc coe cof coo cor cra crb crc cre crf cro crr eaa eab eac eae eaf eao ear eba ebb ebc ebe ebf ebo ebr ec- eca ecb ecc ece ecf eco ecr eea eeb eec eee eef eeo eer ef- efa efb efc efe eff efo efr eo- eoa eob eoc eoe eof eoo eor era erb erc ere erf ero err faa fab fac fae faf fao far fba fbb fbc fbe fbf fbo fbr fca fcb fcc fce fcf fco fcr fea feb fec fee fef feo fer ffa ffc ffe fff ffo ffr foa fob foc foe fof foo for fra frb frc fre frf fro frr oaa oab oac oae oaf oao oar ob- oba obb obc obe obf obo obr oc- oca ocb occ ocf oco ocr oea oeb oec oee oef oeo oer of- ofa ofb ofc ofe off ofo ofr oo- ooa oob ooc oof ooo oor or- ora orb orc ore orf oro orr ra- raa rab rac rae raf rao rar rba rbb rbc rbe rbf rbo rbr rca rcb rcc rce rcf rco rcr re- rea reb rec ree ref reo rer rfa rfb rfc rfe rff rfo rfr roa rob roc roe rof roo ror rra rrb rrc rrf rrr