a-ak aaaa aaab aaac aaba aabb aabc aaca aacb aacc aack aacu aaka aaku abaa abab abac abak abau abb- abba abbb abca abcb abcc abua abuk acaa acab acac acba acca accc accu acu- akaa akca akka akku akua auaa auca baaa baak baba babb babu bac- baca bacc back bak- baka baku bau- bauk bbau bbbb bcaa bcbc bcca bccc bcuc buba bubb bubu buca bucc buck bucu buka bukk buku caaa caab caac caba cabu cac- caca cacc cack caka cauc cauk cbac cbbc cbca cbcc cbcu cbka ccaa ccab ccac ccba ccbc ccca cccb cccc cccu ccuc ckac ckbc ckck cuau cub- cuba cubb cuca cucc cuck cuk- cuka kaaa kaab kaak kaba kabb kabc kabu kacb kacc kacu kaka kakc kakk kaku kau- kaub kauc kauk kbaa kbab kbac kbak kbba kbbb kbbc kbbk kbbu kbca kbcb kbck kbcu kbkb kbkk kbua kbub kbuc kbuk kbuu kcaa kcab kcac kcau kcba kcbc kcbk kcbu kcca kccb kccc kcck kccu kckc kckk kcua kcub kcuk kkaa kkac kkba kkbb kkcb kkck kkkk kkua kkuu kuac kuau kuba kubb kubc kubu kuca kucb kucc kuka kukk kuku kuub kuuk kuuu uabc uaca uaua ubac ubba ucak ucbc ucca ucka ucua ukba ukcc uuuu