a-a a-b a-c aaa aab aac aan aas ab- aba abb abc abn abs ac- aca acb acc acn acs an- ana anb anc ann ans as- asa asb asc asn ass baa bab bac ban bas bba bbb bbc bbn bbs bca bcb bcc bcn bcs bna bnb bnc bnn bns bsa bsb bsc bsn bss c-- caa cab cac can cas cba cbb cbc cbn cbs cca ccb ccc ccn ccs cn- cna cnb cnc cnn cns csa csb csc csn css naa nab nac nan nas nba nbb nbc nbn nbs nca ncb ncc ncn ncs nna nnb nnc nnn nns nsa nsb nsc nsn nss saa sab sac san sas sba sbb sbc sbn sbs sca scb scc scn scs sna snb snc snn sns ss- ssa ssb ssc ssn sss