a-a a-b aaa aab aao aas aau ab- aba abb abo abs abu aoa aob aoo aos aou as- asa asb aso ass asu au- aua aub auo aus b-u baa bab bao bas bau bba bbb bbo bbs bbu boa bob boo bos bou bsa bsb bso bss bsu bua bub buo bus buu oaa oab oao oas oau ob- oba obb obo obs obu oo- ooa oob ooo oos os- osa osb oso oss osu ou- oua ouo ous saa sab sao sas sau sba sbb sbo sbs sbu soa sob soo sos sou ss- ssa ssb sso sss ssu sua sub suo sus suu ua- uaa uab uao uas uau uba ubb ubo ubs ubu uoa uob uoo uos usa usb uso uss usu uua uus uuu