a-a a-b a-t aaa aab aan aas aat ab- aba abb abn abs abt an- ana anb ann ans ant as- asa asb asn ass ast at- ata atb atn ats att baa bab ban bas bat bba bbb bbn bbs bbt bna bnb bnn bns bnt bsa bsb bsn bss bst bta btb btn bts btt naa nab nan nas nat nba nbb nbn nbs nbt nna nnb nnn nns nnt nsa nsb nsn nss nst nta ntb ntn nts ntt saa sab san sas sat sba sbb sbn sbs sbt sna snb snn sns snt ss- ssa ssb ssn sss sst sta stb stn sts stt taa tab tan tas tat tba tbb tbn tbs tbt tna tnb tnn tns tnt tsa tsb tsn tss tst tta ttb ttn tts ttt