c-- ccc ccf cck cco ccr cfc cff cfk cfo cfr ckc cko cky co- coc cof cok coo cor coy crc crf crk cro crr cry cyc cyf cyk cyo cyr fcc fcf fck fco fcr fcy ffc fff ffk ffo ffr ffy fkc fkf fkk foc fof fok foo for foy frc frf frk fro frr fry fy- fyc fyk fyo kcc kck kcr kfc kff kfo kkc kkk kkr kky koc kof kok koo kor koy krc krf krk kro krr kry kyc kyo kyr 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 ory oyo rcc rcf rco rcr rfc rff rfk rfo rfr rkc rkf rkk rko rky roc rof rok roo ror roy rrc rrf rrk rrr ry- ryc ryf ryk ryo ryr ryy ycc ycf yco ycy yfc yff yfr ykk yoc yof yok yoo yor yoy yrc yrf yro yyc yyf yyy