This is the best answer. We could declare 4 to be a prime number, and keep the rest of the definition the same. Instead of just saying "no", you could ask, "ok

This is the best answer. We could declare 4 to be a prime number, and keep the rest of the definition the same. Instead of just saying "no", you could ask, "okay, what would that do for us?" If there isn't a good answer, then what's the point? And usually, you're not in the 1% of 1% of 1%.