a-a a-b a-z aaa aab aao aas aaz ab- aba abb abo abs abz aoa aob aoo aos as- asa asb aso ass asz az- aza azb azo azs azz baa bab bao bas baz bba bbb bbo bbs boa bob boo bos boz bsa bsb bso bss bza bzo bzs bzz oaa oab oao oas ob- oba obb obo obs oo- ooa oob ooo oos os- osa osb oso oss oza ozo ozs ozz saa sab sao sas saz sba sbb sbo sbs soa sob soo sos soz ss- ssa ssb sso sss ssz sza zaa zab zao zas zaz zbb zbs zo- zoa zob zoo zos zsa zsz zzs zzz