c-- ccc ccf cco ccr ccs cfc cff cfo cfr cfs co- coc cof coo cor cos crc crf cro crr crs csc csf cso csr css fcc fcf fco fcr fcs ffc fff ffo ffr ffs foc fof foo for fos frc frf fro frr frs fsc fsf fso fsr fss oc- occ ocf oco ocr ocs of- ofc off ofo ofr ofs oo- ooc oof ooo oor oos or- orc orf oro orr ors os- osc osf oso osr oss rcc rcf rco rcr rcs rfc rff rfo rfr rfs roc rof roo ror ros rrc rrf rrr rrs rsc rsf rso rsr rss scc scf sco scr scs sfc sff sfo sfr sfs soc sof soo sor sos sr- src srf sro srr srs ss- ssc ssf sso ssr sss