a-a a-b a-c aaa aab aac aar aas ab- aba abb abc abr abs ac- aca acb acc acr acs ar- ara arb arc arr ars as- asa asb asc asr ass baa bab bac bar bas bba bbb bbc bbr bbs bca bcb bcc bcr bcs bra brb brr brs bsa bsb bsc bsr bss c-- caa cab cac car cas cba cbb cbc cbr cbs cca ccb ccc ccr ccs cra crb crc crr crs csa csb csc csr css ra- raa rab rac rar ras rba rbb rbc rbr rbs rca rcb rcc rcr rcs rra rrb rrc rrr rrs rsa rsb rsc rsr rss saa sab sac sar sas sba sbb sbc sbr sbs sca scb scc scr scs sr- sra srb src srr srs ss- ssa ssb ssc ssr sss