a-a a-b a-c aaa aab aac aak aay ab- aba abb abc abk aby ac- aca acb acc ack acy aka akb akc akk ay- aya ayc ayk baa bab bac bak bay bba bbb bbc bbk bby bca bcb bcc bck bcy bka bkb bkc bkk by- bya byc byk c-- caa cab cac cak cay cba cbb cbc cbk cby cca ccb ccc cck cka ckb ckc cky cya cyb cyc cyk ka- kaa kab kac kak kay kba kbb kbc kbk kca kcb kcc kck kkb kkc kkk kky kya kyc yaa yab yac yak yay ybc yby yca ycc ycy yka ykk yyb yyc yyy