a-a a-b a-c aaa aab aac aaf aao aas aay ab- aba abb abc abf abo abs aby ac- aca acb acc acf aco acs acy af- afa afb afc aff afo afs afy aoa aob aoc aof aoo aos as- asa asb asc asf aso ass asy ay- aya ayc ayf ayo ays baa bab bac baf bao bas bay bba bbb bbc bbf bbo bbs bby bca bcb bcc bcf bco bcs bcy bfa bfb bfc bff bfo bfs bfy boa bob boc bof boo bos boy bsa bsb bsc bsf bso bss bsy by- bya byc byf byo bys c-- caa cab cac caf cao cas cay cba cbb cbc cbf cbo cbs cby cca ccb ccc ccf cco ccs cfa cfb cfc cff cfo cfs co- coa cob coc cof coo cos coy csa csb csc csf cso css csy cya cyb cyc cyf cyo cys faa fab fac faf fao fas fay fba fbb fbc fbf fbo fbs fca fcb fcc fcf fco fcs fcy ffa ffc fff ffo ffs ffy foa fob foc fof foo fos foy fsa fsb fsc fsf fso fss fy- fya fyb fyc fyo oaa oab oac oaf oao oas ob- oba obb obc obf obo obs oby oc- oca ocb occ ocf oco ocs of- ofa ofb ofc off ofo ofs oo- ooa oob ooc oof ooo oos os- osa osb osc osf oso oss oya oyo oys saa sab sac saf sao sas say sba sbb sbc sbf sbo sbs sby sca scb scc scf sco scs sfa sfb sfc sff sfo sfs soa sob soc sof soo sos soy ss- ssa ssb ssc ssf sso sss sy- sya syb syc sys yaa yab yac yaf yao yas yay ybc ybf ybs yby yca ycc ycf yco ycs ycy yfa yfc yff yfs yob yoc yof yoo yos yoy ysa ysb ysc yso yss ysy yyb yyc yyf yys yyy