a-a a-b a-t aaa aab aas aat aay ab- aba abb abs abt aby as- asa asb ass ast asy at- ata atb ats att ay- aya ays ayt baa bab bas bat bay bba bbb bbs bbt bby bsa bsb bss bst bsy bta btb bts btt bty by- bya bys byt saa sab sas sat say sba sbb sbs sbt sby ss- ssa ssb sss sst sta stb sts stt sty sy- sya syb sys syt taa tab tas tat tay tba tbb tbs tbt tsa tsb tss tst tsy tta ttb tts ttt tty tya tys tyt yaa yab yas yat yay ybs yby ysa ysb yss yst ysy yta yts ytt yyb yys yyt yyy