a-a a-b aaa aab aao aar aay ab- aba abb abo abr aby aoa aob aoo aor ar- ara arb aro arr ary ay- aya ayo ayr baa bab bao bar bay bba bbb bbo bbr bby boa bob boo bor boy bra brb bro brr bry by- bya byo byr oaa oab oao oar ob- oba obb obo obr oby oo- ooa oob ooo oor or- ora orb oro orr ory oya oyo ra- raa rab rao rar ray rba rbb rbo rbr roa rob roo ror roy rra rrb rrr ry- rya ryo ryr ryy yaa yab yao yar yay ybr yby yob yoo yor yoy yra yro yyb yyy