a-a a-b a-c aaa aab aac aad aaf ab- aba abb abc abd abf ac- aca acb acc acd acf ad- ada adb adc add adf af- afa afb afc afd aff baa bab bac bad baf bba bbb bbc bbd bbf bca bcb bcc bcd bcf bda bdb bdc bdd bdf bfa bfb bfc bfd bff c-- caa cab cac cad caf cba cbb cbc cbd cbf cca ccb ccc ccd ccf cda cdb cdc cdd cdf cfa cfb cfc cfd cff daa dab dac dad daf dba dbb dbc dbd dbf dca dcb dcc dcd dcf dda ddb ddc ddd ddf dfa dfb dfc dfd dff faa fab fac fad faf fba fbb fbc fbd fbf fca fcb fcc fcd fcf fda fdb fdc fdd fdf ffa ffc ffd fff