A note about {empty} and NaI...

[Nate Hayes <nh@xxxxxxxxxxxxxxxxx>]

John Pryce wrote:
>   (when given nonsense input); some interval mappings may be allowed
>   to destroy NaI (e.g maybe hull(xx, NaI) should return xx).

I would also just add I believe NaI should always be a true annihilator, 
just like NaN in IEEE 754. This means no interval mapping can destroy the 
NaI. In my view, that is what {empty} is reserved for, i.e., {empty} is 
almost the same as NaI except that for any valid, non-empty interval X

    X \union {empty} = X        but        X \union NaI = NaI.

I think it is important that 1788 will not conflate {empty} and NaI.

Nate