input: Write a function to determine if any two numbers in a given list add up to a specified number. If such a pair exists, return True; otherwise, return False.
  def two_sum(numbers, given):
      for i in range(len(numbers)):
          for j in range(i+1, len(numbers)):
              if numbers[i] + numbers[j] == given:
                  return True
      return False
  
  assert two_sum([1, 2, 3, 4], 5) == True
  assert two_sum([1, 2, 3, 4], 8) == False
  assert two_sum([10, 20, 30, 40], 50) == True
  assert two_sum([1, 3, 5, 7], 10) == True
  assert two_sum([], 0) == False
output: def two_sum(numbers, given):
      for i in range(len(numbers)):
          for j in range(i+1, len(numbers)):
              if numbers[i] + numbers[j] == given:
                  return True
      return False