a-a a-b a-c aaa aab aac aar aay ab- aba abb abc abr aby ac- aca acb acc acr acy ar- ara arb arc arr ary ay- aya ayc ayr baa bab bac bar bay bba bbb bbc bbr bby bca bcb bcc bcr bcy bra brb brr bry by- bya byc byr c-- caa cab cac car cay cba cbb cbc cbr cby cca ccb ccc ccr cra crb crc crr cry cya cyb cyc cyr ra- raa rab rac rar ray rba rbb rbc rbr rca rcb rcc rcr rra rrb rrc rrr ry- rya ryc ryr ryy yaa yab yac yar yay ybc ybr yby yca ycc ycy yra yrc yyb yyc yyy