a-a a-b a-c aaa aab aac aao aay ab- aba abb abc abo aby ac- aca acb acc aco acy aoa aob aoc aoo ay- aya ayc ayo baa bab bac bao bay bba bbb bbc bbo bby bca bcb bcc bco bcy boa bob boc boo boy by- bya byc byo c-- caa cab cac cao cay cba cbb cbc cbo cby cca ccb ccc cco co- coa cob coc coo coy cya cyb cyc cyo oaa oab oac oao ob- oba obb obc obo oby oc- oca ocb occ oco oo- ooa oob ooc ooo oya oyo yaa yab yac yao yay ybc yby yca ycc yco ycy yob yoc yoo yoy yyb yyc yyy