a-a a-b aaa aab aao aar aau aav ab- aba abb abo abr abu abv aoa aob aoo aor aou aov ar- ara arb aro arr aru arv au- aua aub auo aur auv av- ava avb avo avr avu b-u baa bab bao bar bau bav bba bbb bbo bbr bbu boa bob boo bor bou bov bra brb bro brr bru brv bua bub buo bur buu bva bvb bvo bvr bvu bvv oaa oab oao oar oau oav ob- oba obb obo obr obu obv oo- ooa oob ooo oor oov or- ora orb oro orr oru orv ou- oua ouo our ov- ova ovb ovo ovv ra- raa rab rao rar rau rav rba rbb rbo rbr rbu roa rob roo ror rou rov rra rrb rrr rru rua rub ruo rur ruu ruv rva rvb rvo rvr rvu rvv ua- uaa uab uao uar uau uav uba ubb ubo ubr ubu ubv uoa uob uoo uor ur- ura urb uro urr uru uua uur uuu uva uvb uvo uvu uvv v-a vaa vab vao var vau vav vba vbo vbr vbv voa vob voo vor vou vov vra vrb vrr vru vur vuv vva vvb vvo vvr vvv