eee eef eel ees eet eex ef- efe eff efl efs eft efx ele elf ell els elt elx es- ese esf esl ess est esx ete etf etl ets ett etx ex- exe exl exs ext exx fee fef fel fes fet fex ffe fff ffl ffs fft ffx fle flf fll fls flt flx fse fsf fsl fss fst fsx fte ftf ftl fts ftt ftx fxe fxs fxt fxx lee lef lel les let lex lfe lff lfl lfs lft lfx lle llf lll lls llt lse lsf lsl lss lst lte ltf ltl lts ltt ltx lxx se- see sef sel ses set sex sfe sff sfl sfs sft sfx sle slf sll sls slt slx ss- sse ssf ssl sss sst ssx ste stf stl sts stt stx sxl sxs sxt t-x te- tee tef tel tes tet tex tfe tff tfl tfs tft tfx tle tlf tll tls tlt tlx tse tsf tsl tss tst tsx tte ttf ttl tts ttt ttx txe txf txl txs txt xee xel xes xet xex xfe xfl xfs xft xfx xlf xls xlt xsl xss xst xtf xts xtx xxl xxx