-er a-a a-b a-c aaa aab aac aae aan aar ab- aba abb abc abe abn abr ac- aca acb acc ace acn acr aea aeb aec aee aen aer an- ana anb anc ane ann anr ar- ara arb arc are arn arr baa bab bac bae ban bar bba bbb bbc bbe bbn bbr bca bcb bcc bce bcn bcr be- bea beb bec bee ben ber bna bnb bnc bne bnn bnr bra brb bre brn brr c-- caa cab cac cae can car cba cbb cbc cbe cbn cbr cca ccb ccc cce ccn ccr ce- cea ceb cec cee cen cer cn- cna cnb cnc cne cnn cnr cra crb crc cre crn crr eaa eab eac eae ean ear eba ebb ebc ebe ebn ebr ec- eca ecb ecc ece ecn ecr eea eeb eec eee een eer en- ena enb enc ene enn enr era erb erc ere ern err naa nab nac nae nan nar nba nbb nbc nbe nbn nbr nca ncb ncc nce ncn ncr ne- nea neb nec nee nen ner nna nnb nnc nne nnn nra nrb nrc nre nrn nrr ra- raa rab rac rae ran rar rba rbb rbc rbe rbn rbr rca rcb rcc rce rcn rcr re- rea reb rec ree ren rer rna rnb rnc rnn rnr rra rrb rrc rrn rrr