You're right. The "next number" test (under the natural ordering) makes the concept of density obvious, not countability. So I think I've given credence to the

You're right. The "next number" test (under the natural ordering) makes the concept of density obvious, not countability. So I think I've given credence to the notion that those who claim to find something obvious might not fully understand it. Or at least not at four in the morning. (Oh, and a point that Stephen Abbott made in his wonderful intro analysis book now springs to mind: proofs are useful also as a check on our intuition.)