a-a a-b a-c aaa aab aac aas aay ab- aba abb abc abs aby ac- aca acb acc acs acy as- asa asb asc ass asy ay- aya ayc ays baa bab bac bas bay bba bbb bbc bbs bby bca bcb bcc bcs bcy bsa bsb bsc bss bsy by- bya byc bys c-- caa cab cac cas cay cba cbb cbc cbs cby cca ccb ccc ccs csa csb csc css csy cya cyb cyc cys saa sab sac sas say sba sbb sbc sbs sby sca scb scc scs ss- ssa ssb ssc sss sy- sya syb syc sys yaa yab yac yas yay ybc ybs yby yca ycc ycs ycy ysa ysb ysc yss ysy yyb yyc yys yyy