a-a a-b a-t aaa aab aae aas aat ab- aba abb abe abs abt aea aeb aee aes aet as- asa asb ase ass ast at- ata atb ate ats att baa bab bae bas bat bba bbb bbe bbs bbt be- bea beb bee bes bet bsa bsb bse bss bst bta btb bte bts btt eaa eab eae eas eat eba ebb ebe ebs ebt eea eeb eee ees eet es- esa esb ese ess est eta etb ete ets ett saa sab sae sas sat sba sbb sbe sbs sbt se- sea seb see ses set ss- ssa ssb sse sss sst sta stb ste sts stt taa tab tae tas tat tba tbb tbe tbs tbt te- tea teb tee tes tet tsa tsb tse tss tst tta ttb tte tts ttt