code: def black(m):
      
  
      m = float(m)
  
      def f(x):
          if x <= m:
              return 0.0
          return (x - m) / (1.0 - m)
      return f
docs: Return a function that maps all values from [0.0,m] to 0, and maps
      the range [m,1.0] into [0.0, 1.0] linearly.