a-a a-b a-t aaa aab aaf aat aay ab- aba abb abf abt aby af- afa afb aff aft afy at- ata atb atf att ay- aya ayf ayt baa bab baf bat bay bba bbb bbf bbt bby bfa bfb bff bft bfy bta btb btf btt bty by- bya byf byt faa fab faf fat fay fba fbb fbf fbt ffa fff fft ffy fta ftb ftf ftt fty fy- fya fyb taa tab taf tat tay tba tbb tbf tbt tfa tfb tff tft tta ttb ttf ttt tty tya tyf tyt yaa yab yaf yat yay ybf yby yfa yff yft yta ytf ytt yyb yyf yyt yyy