a-a a-b aaa aab aaf aan aao aas ab- aba abb abf abn abo abs af- afa afb aff afn afo afs an- ana anb anf ann ano ans aoa aob aof aon aoo aos as- asa asb asf asn aso ass baa bab baf ban bao bas bba bbb bbf bbn bbo bbs bfa bfb bff bfn bfo bfs bna bnb bnf bnn bno bns boa bob bof bon boo bos bsa bsb bsf bsn bso bss faa fab faf fan fao fas fba fbb fbf fbn fbo fbs ffa fff ffn ffo ffs fna fnb fnf fnn fns foa fob fof fon foo fos fsa fsb fsf fsn fso fss naa nab naf nan nao nas nba nbb nbf nbn nbo nbs nfa nfb nff nfn nfo nfs nna nnb nnf nnn nno nns no- noa nob nof non noo nos nsa nsb nsf nsn nso nss oaa oab oaf oan oao oas ob- oba obb obf obn obo obs of- ofa ofb off ofn ofo ofs on- ona onb onf onn ono ons oo- ooa oob oof oon ooo oos os- osa osb osf osn oso oss saa sab saf san sao sas sba sbb sbf sbn sbo sbs sfa sfb sff sfn sfo sfs sna snb snf snn sno sns soa sob sof son soo sos ss- ssa ssb ssf ssn sso sss