a-a a-b aaa aab aaf aan aas ab- aba abb abf abn abs af- afa afb aff afn afs an- ana anb anf ann ans as- asa asb asf asn ass baa bab baf ban bas bba bbb bbf bbn bbs bfa bfb bff bfn bfs bna bnb bnf bnn bns bsa bsb bsf bsn bss faa fab faf fan fas fba fbb fbf fbn fbs ffa fff ffn ffs fna fnb fnf fnn fns fsa fsb fsf fsn fss naa nab naf nan nas nba nbb nbf nbn nbs nfa nfb nff nfn nfs nna nnb nnf nnn nns nsa nsb nsf nsn nss saa sab saf san sas sba sbb sbf sbn sbs sfa sfb sff sfn sfs sna snb snf snn sns ss- ssa ssb ssf ssn sss