a-a a-b a-c aaa aab aac aak aas aay ab- aba abb abc abk abs aby ac- aca acb acc ack acs acy aka akb akc akk aks as- asa asb asc ask ass asy ay- aya ayc ayk ays baa bab bac bak bas bay bba bbb bbc bbk bbs bby bca bcb bcc bck bcs bcy bka bkb bkc bkk bks bsa bsb bsc bsk bss bsy by- bya byc byk bys c-- caa cab cac cak cas cay cba cbb cbc cbk cbs cby cca ccb ccc cck ccs cka ckb ckc cks cky csa csb csc csk css csy cya cyb cyc cyk cys ka- kaa kab kac kak kas kay kba kbb kbc kbk kbs kca kcb kcc kck kcs kkb kkc kkk kks kky ksa ksb ksc ksk kss kya kyc kys saa sab sac sak sas say sba sbb sbc sbk sbs sby sca scb scc sck scs sk- ska skb skc skk sks sky ss- ssa ssb ssc ssk sss sy- sya syb syc syk sys yaa yab yac yak yas yay ybc ybs yby yca ycc ycs ycy yka ykk ysa ysb ysc ysk yss ysy yyb yyc yys yyy