a-a a-b aaa aab aad aaf aar aas ab- aba abb abd abf abr abs ad- ada adb add adf adr ads af- afa afb afd aff afr afs ar- ara arb ard arf arr ars as- asa asb asd asf asr ass baa bab bad baf bar bas bba bbb bbd bbf bbr bbs bda bdb bdd bdf bdr bds bfa bfb bfd bff bfr bfs bra brb brd brf brr brs bsa bsb bsd bsf bsr bss daa dab dad daf dar das dba dbb dbd dbf dbr dbs dda ddb ddd ddf ddr dds dfa dfb dfd dff dfr dfs dra drb drd drr drs dsa dsb dsd dsf dsr dss faa fab fad faf far fas fba fbb fbd fbf fbr fbs fda fdb fdd fdf fdr fds ffa ffd fff ffr ffs fra frb frd frf frr frs fsa fsb fsd fsf fsr fss ra- raa rab rad raf rar ras rba rbb rbd rbf rbr rbs rda rdb rdd rdf rdr rds rfa rfb rfd rff rfr rfs rra rrb rrd rrf rrr rrs rsa rsb rsd rsf rsr rss saa sab sad saf sar sas sba sbb sbd sbf sbr sbs sda sdb sdd sdf sdr sds sfa sfb sfd sff sfr sfs sr- sra srb srd srf srr srs ss- ssa ssb ssd ssf ssr sss