-er c-- ccc cce ccf cco ccr ccs ce- cec cee cef ceo cer ces cfc cfe cff cfo cfr cfs co- coc coe cof coo cor cos crc cre crf cro crr crs csc cse csf cso csr css ec- ecc ece ecf eco ecr ecs eec eee eef eeo eer ees ef- efc efe eff efo efr efs eo- eoc eoe eof eoo eor eos erc ere erf ero err ers es- esc ese esf eso esr ess fcc fce fcf fco fcr fcs fec fee fef feo fer fes ffc ffe fff ffo ffr ffs foc foe fof foo for fos frc fre frf fro frr frs fsc fse fsf fso fsr fss oc- occ ocf oco ocr ocs oec oee oef oeo oer oes of- ofc ofe off ofo ofr ofs oo- ooc oof ooo oor oos or- orc ore orf oro orr ors os- osc ose osf oso osr oss rcc rce rcf rco rcr rcs re- rec ree ref reo rer res rfc rfe rff rfo rfr rfs roc roe rof roo ror ros rrc rrf rrr rrs rsc rse rsf rso rsr rss scc sce scf sco scr scs se- sec see sef seo ser ses sfc sfe sff sfo sfr sfs soc soe sof soo sor sos sr- src sre srf sro srr srs ss- ssc sse ssf sso ssr sss