a-a a-b a-c aaa aab aac aad aak ab- aba abb abc abd abk ac- aca acb acc acd ack ad- ada adb adc add adk aka akb akc akd akk baa bab bac bad bak bba bbb bbc bbd bbk bca bcb bcc bcd bck bda bdb bdc bdd bdk bka bkb bkc bkk c-- caa cab cac cad cak cba cbb cbc cbd cbk cca ccb ccc ccd cck cda cdb cdc cdd cdk cka ckb ckc ckd daa dab dac dad dak dba dbb dbc dbd dbk dca dcb dcc dcd dck dda ddb ddc ddd ddk dka dkb dkc dkk ka- kaa kab kac kad kak kba kbb kbc kbd kbk kca kcb kcc kcd kck kda kdb kdc kdk kkb kkc kkk