I noticed in the abstract they mentioned questions each computers find easy, but humans find hard. This is especially useful where you want to identify that th

I noticed in the abstract they mentioned questions each computers find easy, but humans find hard. This is especially useful where you want to identify that the user is not a bot. For example, ask for 7492 × 4812. Computers will do this quickly. Humans [1] need to open the calculator, type in the number, type out the reply, and so on. In other words its not the reply that is important, its the time taken to get to the reply. Mind you this only works until the AI-pretending-to-be-human cottons on. Then again, Asimov made a career documenting edge cases for robots trying to deceive. [1] Well most of them anyway