eee eef ees eet eex ef- efe eff efi efs eft efx eie eif eii eis eit eix es- ese esf esi ess est esx ete etf eti ets ett etx ex- exe exi exs ext exx fee fef fei fes fet fex ffe fff ffi ffs fft ffx fie fif fii fis fit fix fse fsf fsi fss fst fsx fte ftf fti fts ftt ftx fxe fxi fxs fxt fxx i-f ie- iee ief iei ies iet iex ife iff ifi ifs ift ifx iie iif iii iis iit iix is- ise isf isi iss ist ite itf iti its itt itx ixe ixi se- see sef sei ses set sex sfe sff sfi sfs sft sfx sie sif sii sis sit six ss- sse ssf ssi sss sst ssx ste stf sti sts stt stx sxi sxs sxt t-x te- tee tef tei tes tet tex tfe tff tfi tfs tft tfx tie tif tii tis tit tix tse tsf tsi tss tst tsx tte ttf tti tts ttt ttx txe txf txi txs txt xee xes xet xex xfe xfs xft xfx xie xii xis xit xix xsi xss xst xtf xti xts xtx xxi xxx