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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def lowpass(cutoff):
 """ This strategy uses an exponential approximation for cut-off frequency calculation, found by matching the single pole and single zero Laplace highpass filter and mirroring the resulting filter to get a lowpass. """

  R = thub(exp(cutoff - pi), 2)
  G = (R + 1) / 2
  return G * (1 + z ** -1) / (1 + R * z ** -1)