-er c-- ccc cce cck cco ccr ccx ce- cec cee cek ceo cer cex ckc cko ckx co- coc coe cok coo cor cox crc cre crk cro crr crx cxc cxk cxo cxr cxx ec- ecc ece eck eco ecr ecx eec eee eek eeo eer eex ekc eke eko ekr eo- eoc eoe eok eoo eor erc ere erk ero err ex- exc exe exo exr exx kcc kce kck kcr kcx ke- kec kee kek keo ker kex kkc kke kkk kkr koc koe kok koo kor krc krk kro krr kxo oc- occ ock oco ocr ocx oec oee oeo oer oex okc oke okk oko okr oo- ooc ook ooo oor oox or- orc ore ork oro orr orx ox- oxc oxo oxx rcc rce rco rcr rcx re- rec ree rek reo rer rex rkc rke rkk rko roc roe rok roo ror rox rrc rrk rrr rxr xcr xcx xee xer xex xke xoc xok xoo xor xox xrc xrx xxo xxx