c-- ccc cck cco ccr ccs ckc cko cks co- coc cok coo cor cos crc crk cro crr crs csc csk cso csr css kcc kck kcr kcs kkc kkk kkr kks koc kok koo kor kos krc krk kro krr krs ksc ksk kso ksr kss oc- occ ock oco ocr ocs okc okk oko okr oks oo- ooc ook ooo oor oos or- orc ork oro orr ors os- osc osk oso osr oss rcc rco rcr rcs rkc rkk rko rks roc rok roo ror ros rrc rrk rrr rrs rsc rsk rso rsr rss scc sck sco scr scs sk- skc skk sko skr sks soc sok soo sor sos sr- src srk sro srr srs ss- ssc ssk sso ssr sss