a-a a-b a-c aaa aab aac aan aar ab- aba abb abc abn abr ac- aca acb acc acn acr an- ana anb anc ann anr ar- ara arb arc arn arr baa bab bac ban bar bba bbb bbc bbn bbr bca bcb bcc bcn bcr bna bnb bnc bnn bnr bra brb brn brr c-- caa cab cac can car cba cbb cbc cbn cbr cca ccb ccc ccn ccr cn- cna cnb cnc cnn cnr cra crb crc crn crr naa nab nac nan nar nba nbb nbc nbn nbr nca ncb ncc ncn ncr nna nnb nnc nnn nra nrb nrc nrn nrr ra- raa rab rac ran rar rba rbb rbc rbn rbr rca rcb rcc rcn rcr rna rnb rnc rnn rnr rra rrb rrc rrn rrr