a-a a-b a-i aaa aab aai aar aax ab- aba abb abi abr abx ai- aia aib aii air aix ar- ara arb ari arr arx ax- axa axi axr axx baa bab bai bar bax bba bbb bbi bbr bbx bi- bia bib bii bir bix bra brb bri brr brx bxb bxi bxx ia- iaa iab iai iar iba ibb ibi ibr ibx iia iib iii iir iix ir- ira irb iri irr irx ixi ra- raa rab rai rar rax rba rbb rbi rbr rbx ria rib rii rir rix rra rrb rri rrr rxr xaa xar xbr xbx xia xii xix xrx xxi xxx