-er c-- ccc cce ccf cco ccr ccx ce- cec cee cef ceo cer cex cfc cfe cff cfo cfr cfx co- coc coe cof coo cor cox crc cre crf cro crr crx cxc cxf cxo cxr cxx ec- ecc ece ecf eco ecr ecx eec eee eef eeo eer eex ef- efc efe eff efo efr efx eo- eoc eoe eof eoo eor erc ere erf ero err ex- exc exe exo exr exx fcc fce fcf fco fcr fcx fec fee fef feo fer fex ffc ffe fff ffo ffr ffx foc foe fof foo for fox frc fre frf fro frr fxe fxr fxx oc- occ ocf oco ocr ocx oec oee oef oeo oer oex of- ofc ofe off ofo ofr ofx oo- ooc oof ooo oor oox or- orc ore orf oro orr orx ox- oxc oxf oxo oxx rcc rce rcf rco rcr rcx re- rec ree ref reo rer rex rfc rfe rff rfo rfr roc roe rof roo ror rox rrc rrf rrr rxr xcf xcr xcx xee xer xex xfe xfx xoc xof xoo xor xox xrc xrf xrx xxo xxx