WORST_CASE(?,O(n^1))

Solution:
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  "0" :: [] -(0)-> "a"(1)
  "p" :: ["a"(1) x "a"(1) x "a"(1)] -(1)-> "a"(0)
  "s" :: ["a"(1)] -(1)-> "a"(1)


Cost Free Signatures:
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