input: Write a function to find out if any two numbers in a given list add up to a specified number. Return True if such a pair exists, else 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([3, 5, 2, -4, 8, 11], 7)==True
  assert two_sum([3, 5, 2, -4, 8, 11], 23)==False
  assert two_sum([1, 1, 1, 1], 2)==True
  assert two_sum([], 0)==False
  assert two_sum([5, 5], 10)==True
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