a-a a-b aaa aab aaf aar aay ab- aba abb abf abr aby af- afa afb aff afr afy ar- ara arb arf arr ary ay- aya ayf ayr baa bab baf bar bay bba bbb bbf bbr bby bfa bfb bff bfr bfy bra brb brf brr bry by- bya byf byr faa fab faf far fay fba fbb fbf fbr ffa fff ffr ffy fra frb frf frr fry fy- fya fyb ra- raa rab raf rar ray rba rbb rbf rbr rfa rfb rff rfr rra rrb rrf rrr ry- rya ryf ryr ryy yaa yab yaf yar yay ybf ybr yby yfa yff yfr yra yrf yyb yyf yyy