a-a a-b aaa aab aar aau aax ab- aba abb abr abu abx ar- ara arb arr aru arx au- aua aub aur aux ax- axa axr axx b-u baa bab bar bau bax bba bbb bbr bbu bbx bra brb brr bru brx bua bub bur buu bux bxb bxx ra- raa rab rar rau rax rba rbb rbr rbu rbx rra rrb rrr rru rua rub rur ruu rux rxr ua- uaa uab uar uau uba ubb ubr ubu ubx ur- ura urb urr uru urx uua uur uuu uxb uxr uxu xaa xar xau xbr xbx xrx xxx