a-a a-b a-i aaa aab aai aao aar ab- aba abb abi abo abr ai- aia aib aii aio air aoa aob aoi aoo aor ar- ara arb ari aro arr baa bab bai bao bar bba bbb bbi bbo bbr bi- bia bib bii bio bir boa bob boi boo bor bra brb bri bro brr ia- iaa iab iai iao iar iba ibb ibi ibo ibr iia iib iii iio iir io- ioa iob ioi ioo ior ir- ira irb iri iro irr o-i oaa oab oai oao oar ob- oba obb obi obo obr oia oib oii oio oir oo- ooa oob ooi ooo oor or- ora orb ori oro orr ra- raa rab rai rao rar rba rbb rbi rbo rbr ria rib rii rio rir roa rob roi roo ror rra rrb rri rrr