a-a a-b a-i aaa aab aai aao aax aay ab- aba abb abi abo abx aby ai- aia aib aii aio aix aiy aoa aob aoi aoo aox ax- axa axi axo axx ay- aya ayi ayo ayx baa bab bai bao bax bay bba bbb bbi bbo bbx bby bi- bia bib bii bio bix biy boa bob boi boo box boy bxb bxi bxo bxx by- bya byi byo ia- iaa iab iai iao iba ibb ibi ibo ibx iby iia iib iii iio iix io- ioa iob ioi ioo ixi ixy iya iyo iyy o-i oaa oab oai oao oax ob- oba obb obi obo obx oby oia oib oii oio oo- ooa oob ooi ooo oox ox- oxa oxb oxi oxo oxx oxy oya oyi oyo xaa xbx xia xii xio xix xoa xoi xoo xox xxi xxo xxx xxy xyy yaa yab yai yao yax yay ybi yby yii yio yob yoi yoo yox yoy yxa yxy yyb yyy