-er eee eef eeo eer ees eex ef- efe eff efo efr efs efx eo- eoe eof eoo eor eos ere erf ero err ers es- ese esf eso esr ess esx ex- exe exo exr exs exx fee fef feo fer fes fex ffe fff ffo ffr ffs ffx foe fof foo for fos fox fre frf fro frr frs fse fsf fso fsr fss fsx fxe fxr fxs fxx oee oef oeo oer oes oex of- ofe off ofo ofr ofs ofx oo- oof ooo oor oos oox or- ore orf oro orr ors orx os- ose osf oso osr oss osx ox- oxf oxo oxx re- ree ref reo rer res rex rfe rff rfo rfr rfs roe rof roo ror ros rox rrf rrr rrs rse rsf rso rsr rss rsx rxr rxs se- see sef seo ser ses sex sfe sff sfo sfr sfs sfx soe sof soo sor sos sox sr- sre srf sro srr srs srx ss- sse ssf sso ssr sss ssx sxs xee xer xes xex xfe xfs xfx xof xoo xor xos xox xrf xrx xss xxo xxx