a-a a-b a-i a-t aaa aab aai aas aat ab- aba abb abi abs abt ai- aia aib aii ais ait as- asa asb asi ass ast at- ata atb ati ats att baa bab bai bas bat bba bbb bbi bbs bbt bi- bia bib bii bis bit bsa bsb bsi bss bst bta btb bti bts btt ia- iaa iab iai ias iat iba ibb ibi ibs ibt iia iib iii iis iit is- isa isb isi iss ist ita itb iti its itt saa sab sai sas sat sba sbb sbi sbs sbt sia sib sii sis sit ss- ssa ssb ssi sss sst sta stb sti sts stt taa tab tai tas tat tba tbb tbi tbs tbt tia tib tii tis tit tsa tsb tsi tss tst tta ttb tti tts ttt