input: Write a function to check if any two numbers from a given list sum up to a specified target number. If such a pair exists, return True, otherwise return False. If the list is empty or if it contains fewer than two elements, return False.
  assert check_sum([1, 2, 3, 4, 5], 9)==True
  assert check_sum([10, 15, 3, 7], 17)==True
  assert check_sum([4, 6, 8], 12)==False
  assert check_sum([5], 5)==False
  assert check_sum([], 0)==False
output: def check_sum(nums, target):
      if len(nums) < 2:
          return False
      seen = set()
      for num in nums:
          if target - num in seen:
              return True
          seen.add(num)
      return False