input: def calculate_sum_using_lambda(a: int, b: int) -> callable:
      """ Suggest a valid Python syntax to calculate the sum of two variables using lambda.
      >>> sum_function = calculate_sum_using_lambda(3, 4)
      >>> print(sum_function(3, 4))
      7
      """
      return lambda x, y: x + y
output:     return lambda x, y: x + y