-er eee eef eer ees eex ef- efe eff efi efr efs efx eie eif eii eir eis eix ere erf eri err ers es- ese esf esi esr ess esx ex- exe exi exr exs exx fee fef fei fer fes fex ffe fff ffi ffr ffs ffx fie fif fii fir fis fix fre frf fri frr frs fse fsf fsi fsr fss fsx fxe fxi fxr fxs fxx i-f ie- iee ief iei ier ies iex ife iff ifi ifr ifs ifx iie iif iii iir iis iix ir- ire irf iri irr irs irx is- ise isf isi isr iss ixe ixi re- ree ref rei rer res rex rfe rff rfi rfr rfs rie rif rii rir ris rix rrf rri rrr rrs rse rsf rsi rsr rss rsx rxr rxs se- see sef sei ser ses sex sfe sff sfi sfr sfs sfx sie sif sii sir sis six sr- sre srf sri srr srs srx ss- sse ssf ssi ssr sss ssx sxi sxs xee xer xes xex xfe xfs xfx xie xii xis xix xrf xrx xsi xss xxi xxx