a-a a-b a-c aaa aab aac aak aau ab- aba abb abc abk abu ac- aca acb acc ack acu aka akb akc akk aku au- aua aub auc auk b-u baa bab bac bak bau bba bbb bbc bbk bbu bca bcb bcc bck bcu bka bkb bkc bkk bua bub buc buk buu c-- caa cab cac cak cau cba cbb cbc cbk cbu cca ccb ccc cck ccu cka ckb ckc cua cub cuc cuk cuu ka- kaa kab kac kak kau kba kbb kbc kbk kbu kca kcb kcc kck kcu kkb kkc kkk kku kub kuc kuk kuu ua- uaa uab uac uak uau uba ubb ubc ubk ubu uca ucb ucc uck ucu uka ukb ukc ukk uku uua uuc uuu