input: from typing import Callable
  
  def sum_with_lambda(a: int, b: int) -> Callable[[], int]:
      """ Returns a lambda function that calculates the sum of two variables a and b.
      >>> sum_with_lambda(3, 4)()
      7
      >>> sum_with_lambda(5, 10)()
      15
      """
      return lambda: a + b
output:     return lambda: a + b