-er eee eef eem eer ees eet eex ef- efe eff efm efr efs eft efx em- eme emf emm emr ems emt emx ere erf erm err ers ert es- ese esf esm esr ess est esx ete etf etm etr ets ett etx ex- exe exr exs ext exx fee fef fem fer fes fet fex ffe fff ffm ffr ffs fft ffx fme fmf fmm fmr fms fmt fmx fre frf frm frr frs frt fse fsf fsm fsr fss fst fsx fte ftf ftm ftr fts ftt ftx fxe fxm fxr fxs fxt fxx m-f m-r mee mef mem mer mes met mex mfe mff mfm mfr mfs mft mme mmf mmm mmr mms mmt mmx mre mrf mrm mrr mrs mrt mrx mse msf msm msr mss mst msx mte mtf mtm mtr mts mtt mtx mxr mxs re- ree ref rem rer res ret rex rfe rff rfm rfr rfs rft rme rmf rmm rmr rms rmt rmx rrf rrm rrr rrs rrt rse rsf rsm rsr rss rst rsx rte rtf rtm rtr rts rtt rtx rxr rxs se- see sef sem ser ses set sex sfe sff sfm sfr sfs sft sfx sme smf smm smr sms smt smx sr- sre srf srm srr srs srt srx ss- sse ssf ssm ssr sss sst ssx ste stf stm str sts stt stx sxm sxs sxt t-x te- tee tef tem ter tes tet tex tfe tff tfm tfr tfs tft tfx tme tmf tmm tmr tms tmt tmx tre trf trm trr trs trt trx tse tsf tsm tsr tss tst tsx tte ttf ttm ttr tts ttt ttx txe txf txs txt xee xem xer xes xet xex xfe xfm xfs xft xfx xmf xmm xmr xms xmt xmx xrf xrt xrx xsm xss xst xtf xtm xtr xts xtx xxx