c-- ccc ccf cck cco ccr cfc cff cfk cfo cfr ckc cko co- coc cof cok coo cor crc crf crk cro crr fcc fcf fck fco fcr ffc fff ffk ffo ffr fkc fkf fkk foc fof fok foo for frc frf frk fro frr kcc kck kcr kfc kff kfo kkc kkk kkr koc kof kok koo kor krc krf krk kro krr oc- occ ocf ock oco ocr of- ofc off ofo ofr okc okk oko okr oo- ooc oof ook ooo oor or- orc orf ork oro orr rcc rcf rco rcr rfc rff rfk rfo rfr rkc rkf rkk rko roc rof rok roo ror rrc rrf rrk rrr