WORST_CASE(?,O(n^1))

Solution:
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  "0" :: [] -(0)-> "a"(4)
  "0" :: [] -(0)-> "a"(0)
  "bits" :: ["a"(4)] -(1)-> "a"(0)
  "half" :: ["a"(4)] -(2)-> "a"(4)
  "s" :: ["a"(4)] -(4)-> "a"(4)
  "s" :: ["a"(0)] -(0)-> "a"(0)


Cost Free Signatures:
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