a-a a-b a-c aaa aab aac aas aau ab- aba abb abc abs abu ac- aca acb acc acs acu as- asa asb asc ass asu au- aua aub auc aus b-u baa bab bac bas bau bba bbb bbc bbs bbu bca bcb bcc bcs bcu bsa bsb bsc bss bsu bua bub buc bus buu c-- caa cab cac cas cau cba cbb cbc cbs cbu cca ccb ccc ccs ccu csa csb csc css csu cua cub cuc cus cuu saa sab sac sas sau sba sbb sbc sbs sbu sca scb scc scs scu ss- ssa ssb ssc sss ssu sua sub suc sus suu ua- uaa uab uac uas uau uba ubb ubc ubs ubu uca ucb ucc ucs ucu usa usb usc uss usu uua uuc uus uuu