a-a a-b aaa aab aan aar aau ab- aba abb abn abr abu an- ana anb ann anr anu ar- ara arb arn arr aru au- aua aub aun aur b-u baa bab ban bar bau bba bbb bbn bbr bbu bna bnb bnn bnr bnu bra brb brn brr bru bua bub bun bur buu naa nab nan nar nau nba nbb nbn nbr nbu nna nnb nnn nnu nra nrb nrn nrr nru nua nub nun nur nuu ra- raa rab ran rar rau rba rbb rbn rbr rbu rna rnb rnn rnr rnu rra rrb rrn rrr rru rua rub run rur ruu ua- uaa uab uan uar uau uba ubb ubn ubr ubu un- una unb unn unr unu ur- ura urb urn urr uru uua uun uur uuu