-er a-a a-b a-c aaa aab aac aae aar ab- aba abb abc abe abr ac- aca acb acc ace acr aea aeb aec aee aer ar- ara arb arc are arr baa bab bac bae bar bba bbb bbc bbe bbr bca bcb bcc bce bcr be- bea beb bec bee ber bra brb bre brr c-- caa cab cac cae car cba cbb cbc cbe cbr cca ccb ccc cce ccr ce- cea ceb cec cee cer cra crb crc cre crr eaa eab eac eae ear eba ebb ebc ebe ebr ec- eca ecb ecc ece ecr eea eeb eec eee eer era erb erc ere err ra- raa rab rac rae rar rba rbb rbc rbe rbr rca rcb rcc rce rcr re- rea reb rec ree rer rra rrb rrc rrr