a-a a-b aaa aab aad aaf aas ab- aba abb abd abf abs ad- ada adb add adf ads af- afa afb afd aff afs as- asa asb asd asf ass baa bab bad baf bas bba bbb bbd bbf bbs bda bdb bdd bdf bds bfa bfb bfd bff bfs bsa bsb bsd bsf bss daa dab dad daf das dba dbb dbd dbf dbs dda ddb ddd ddf dds dfa dfb dfd dff dfs dsa dsb dsd dsf dss faa fab fad faf fas fba fbb fbd fbf fbs fda fdb fdd fdf fds ffa ffd fff ffs fsa fsb fsd fsf fss saa sab sad saf sas sba sbb sbd sbf sbs sda sdb sdd sdf sds sfa sfb sfd sff sfs ss- ssa ssb ssd ssf sss