input: Write a function to find out if any two numbers in a given list add up to a specified target 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([0, 0, 1, 2], 0)==True
  assert two_sum([3, 1, 2, 4], 6)==True
  assert two_sum([], 10)==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