a-a a-b aaa aab aao aas aay ab- aba abb abo abs aby aoa aob aoo aos as- asa asb aso ass asy ay- aya ayo ays baa bab bao bas bay bba bbb bbo bbs bby boa bob boo bos boy bsa bsb bso bss bsy by- bya byo bys oaa oab oao oas ob- oba obb obo obs oby oo- ooa oob ooo oos os- osa osb oso oss oya oyo oys saa sab sao sas say sba sbb sbo sbs sby soa sob soo sos soy ss- ssa ssb sso sss sy- sya syb sys yaa yab yao yas yay ybs yby yob yoo yos yoy ysa ysb yso yss ysy yyb yys yyy