new_contents: import numpy as np
  from scipy.stats import chi2
  from graphbutler import recipe, save_all, Graph, Parameterized
  
  @recipe
  def chi_squared_pdf():
      g = Graph()
      g.title = "Chi-squared probability distribution"
      g.x = np.arange(0.0, 9.0, 0.01)
  
      def y(k):
          y = chi2.pdf(g.x, k)
          # Value threshold because k=1 is unbounded
          y[y > 0.5] = np.nan
          return y
  
      g.y = Parameterized("k", y, (1, 2, 3, 5, 9))
      return g
  
  if __name__ == "__main__":
      # chi_squared_pdf().show()
      save_all()
  
subject: Add chi-squared pdf example