a-a a-b aaa aab aaf aan aar aas ab- aba abb abf abn abr abs af- afa afb aff afn afr afs an- ana anb anf ann anr ans ar- ara arb arf arn arr ars as- asa asb asf asn asr ass baa bab baf ban bar bas bba bbb bbf bbn bbr bbs bfa bfb bff bfn bfr bfs bna bnb bnf bnn bnr bns bra brb brf brn brr brs bsa bsb bsf bsn bsr bss faa fab faf fan far fas fba fbb fbf fbn fbr fbs ffa fff ffn ffr ffs fna fnb fnf fnn fnr fns fra frb frf frn frr frs fsa fsb fsf fsn fsr fss naa nab naf nan nar nas nba nbb nbf nbn nbr nbs nfa nfb nff nfn nfr nfs nna nnb nnf nnn nns nra nrb nrf nrn nrr nrs nsa nsb nsf nsn nsr nss ra- raa rab raf ran rar ras rba rbb rbf rbn rbr rbs rfa rfb rff rfn rfr rfs rna rnb rnn rnr rns rra rrb rrf rrn rrr rrs rsa rsb rsf rsn rsr rss saa sab saf san sar sas sba sbb sbf sbn sbr sbs sfa sfb sff sfn sfr sfs sna snb snf snn snr sns sr- sra srb srf srn srr srs ss- ssa ssb ssf ssn ssr sss