a-ak a-ok aaaa aaab aaac aaba aabb aabc aaca aacb aacc aack aaco aaka aaoo abaa abab abac abak abb- abba abbb abbo abca abcb abcc aboa abob abok aboo acaa acab acac acba acca accc acco acoa akaa akao akca akka akko akok aoba aoca baaa baak baba babb babo bac- baca bacc back baco bak- baka bako bbbb bcaa bcbc bcca bccc boab boac boak boba bobb bobo boca bock boco boka boko boob booc book c-bo caaa caab caac caba cabo cac- caca cacc cack caco caka cbac cbbc cbca cbcc cbka cbko ccaa ccab ccac ccba ccbc ccca cccb cccc ccob ccoc ckac ckbc ckck ckco ckoa ckob ckoc ckoo coak coba cobb cobo coca cock coco cok- coka coko coob cook kaaa kaab kaak kaba kabb kabc kabo kacb kacc kaco kaka kakc kakk kako kaoa kaoc kaok kbaa kbab kbac kbak kbba kbbb kbbc kbbk kbbo kbca kbcb kbck kbco kbkb kbkk kbko kboa kbob kboc kbok kboo kcaa kcab kcac kcba kcbc kcbk kcca kccb kccc kcck kckc kckk kcko kcob kkaa kkac kkba kkbb kkbo kkcb kkck kkco kkkk kkoa kkob kkoo koab koac koak koba kobb kobc kobk kobo koca kocb kock koka kokb kokc kokk koko koob kooc kook kooo obak obba obbo obkb obok ocab ocac ocak ocbc occa occc okak okka okko okok ooaa ooak ooba oooo