bbb bbi bbo bbr bbx bi- bib bii bio bir bix bob boi boo bor box brb bri bro brr brx bxb bxi bxo bxx ibb ibi ibo ibr ibx iib iii iio iir iix io- iob ioi ioo ior ir- irb iri iro irr irx ixi o-i ob- obb obi obo obr obx oib oii oio oir oo- oob ooi ooo oor oox or- orb ori oro orr orx ox- oxb oxi oxo oxx rbb rbi rbo rbr rbx rib rii rio rir rix rob roi roo ror rox rrb rri rrr rxr xbr xbx xii xio xix xoi xoo xor xox xrx xxi xxo xxx