input: def understand_recursion_factorial(n: int) -> int:
      """
      Define a recursive function to calculate the factorial of a number.
      >>> understand_recursion_factorial(5)
      120
      >>> understand_recursion_factorial(3)
      6
      """
      if n == 1:
          return 1
      else:
          return n * understand_recursion_factorial(n - 1)
output:     if n == 1:
          return 1
      else:
          return n * understand_recursion_factorial(n - 1)