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```elixir

     

       
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defmodule Signal do

     

       
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  def compare([], []), do: :eq

     

       
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  def compare([], [_ | _]), do: :lt

     

       
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  def compare(a, a), do: :eq

     

       
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  def compare(a, b) when is_integer(a) and is_integer(b) and a < b, do: :lt

     

       
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  def compare([], [_ | _]), do: :lt

     

       
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  def compare([a | as], [b | bs]), do: with(:eq <- compare(a, b), do: compare(as, bs))

     

       
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  def compare(a, b)