a-a a-b a-c aaa aab aac aan aao aas ab- aba abb abc abn abo abs ac- aca acb acc acn aco acs an- ana anb anc ann ano ans aoa aob aoc aon aoo aos as- asa asb asc asn aso ass baa bab bac ban bao bas bba bbb bbc bbn bbo bbs bca bcb bcc bcn bco bcs bna bnb bnc bnn bno bns boa bob boc bon boo bos bsa bsb bsc bsn bso bss c-- caa cab cac can cao cas cba cbb cbc cbn cbo cbs cca ccb ccc ccn cco ccs cn- cna cnb cnc cnn cno cns co- coa cob coc con coo cos csa csb csc csn cso css naa nab nac nan nao nas nba nbb nbc nbn nbo nbs nca ncb ncc ncn nco ncs nna nnb nnc nnn nno nns no- noa nob noc non noo nos nsa nsb nsc nsn nso nss oaa oab oac oan oao oas ob- oba obb obc obn obo obs oc- oca ocb occ ocn oco ocs on- ona onb onc onn ono ons oo- ooa oob ooc oon ooo oos os- osa osb osc osn oso oss saa sab sac san sao sas sba sbb sbc sbn sbo sbs sca scb scc scn sco scs sna snb snc snn sno sns soa sob soc son soo sos ss- ssa ssb ssc ssn sso sss