input: from typing import List
  
  def max_revenue(prices: List[int]) -> int:
      """ Calculate the maximum revenue that can be obtained from a list of prices,
      where the revenue is defined as the difference between the highest and the lowest
      price in any possible sequence of transactions.
      >>> max_revenue([10, 7, 5, 8, 11, 9])
      6
      """
      diff = [prices[i + 1] - prices[i] for i in range(len(prices) - 1)] 
      max_diff = 0
      for i in range(len(diff)): 
          for j in range(i + 1, len(diff) + 1): 
              current_diff = sum(diff[i:j]) 
              if current_diff > max_diff: 
                  max_diff = current_diff 
   
      return max_diff
output:     
      if max_diff == 0:
          return 0
      else:
          return max_diff + 1
  