a-a a-b aaa aab aad aao aas ab- aba abb abd abo abs ad- ada adb add ado ads aoa aob aod aoo aos as- asa asb asd aso ass baa bab bad bao bas bba bbb bbd bbo bbs bda bdb bdd bdo bds boa bob bod boo bos bsa bsb bsd bso bss daa dab dad dao das dba dbb dbd dbo dbs dda ddb ddd ddo dds doa dob dod doo dos dsa dsb dsd dso dss oaa oab oad oao oas ob- oba obb obd obo obs oda odb odd odo ods oo- ooa oob ood ooo oos os- osa osb osd oso oss saa sab sad sao sas sba sbb sbd sbo sbs sda sdb sdd sdo sds soa sob sod soo sos ss- ssa ssb ssd sso sss