a-ak a-ok aaaa aaab aaba aabb aaka aaoo abaa abab abak abb- abba abbb abbo aboa abob abok aboo akaa akao akka akko akok aoba baaa baak baba babb babo bak- baka bako bbbb boab boak boba bobb bobo boka boko boob book kaaa kaab kaak kaba kabb kabo kaka kakk kako kaoa kaok kbaa kbab kbak kbba kbbb kbbk kbbo kbkb kbkk kbko kboa kbob kbok kboo kkaa kkba kkbb kkbo kkkk kkoa kkob kkoo koab koak koba kobb kobk kobo koka kokb kokk koko koob kook kooo obak obba obbo obkb obok okak okka okko okok ooaa ooak ooba oooo