c-- ccc ccf cck cco ccr ccx cfc cff cfk cfo cfr cfx ckc cko ckx co- coc cof cok coo cor cox crc crf crk cro crr crx cxc cxf cxk cxo cxr cxx fcc fcf fck fco fcr fcx ffc fff ffk ffo ffr ffx fkc fkf fkk foc fof fok foo for fox frc frf frk fro frr fxr fxx kcc kck kcr kcx kfc kff kfo kfx kkc kkk kkr koc kof kok koo kor krc krf krk kro krr kxo oc- occ ocf ock oco ocr ocx of- ofc off ofo ofr ofx okc okk oko okr oo- ooc oof ook ooo oor oox or- orc orf ork oro orr orx ox- oxc oxf oxo oxx rcc rcf rco rcr rcx rfc rff rfk rfo rfr rkc rkf rkk rko roc rof rok roo ror rox rrc rrf rrk rrr rxr xcf xcr xcx xfx xoc xof xok xoo xor xox xrc xrf xrx xxo xxx