WORST_CASE(?,O(n^2))

Solution:
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  "0" :: [] -(0)-> "A"(2, 2)
  "0" :: [] -(0)-> "A"(4, 2)
  "f" :: ["A"(2, 2)] -(3)-> "A"(2, 2)
  "s" :: ["A"(4, 2)] -(2)-> "A"(2, 2)
  "s" :: ["A"(6, 2)] -(4)-> "A"(4, 2)


Cost Free Signatures:
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  "0" :: [] -(0)-> "A"_cf(0, 0)
  "f" :: ["A"_cf(0, 0)] -(0)-> "A"_cf(0, 0)
  "s" :: ["A"_cf(0, 0)] -(0)-> "A"_cf(0, 0)


Base Constructors:
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