On 23 Nov 2022, at 16:56, denis walker wrote:
One empty set is the same as any other empty set. We only need one clearly defined and easily recognisable empty set and we have that, AS-NULL. If I create an empty set, AS-WALKER it doesn't do anything that AS-NULL can't do.
Sure. What I have in mind is AS-NIALLSPECIAL, which I populate with a list of AS numbers which I want to advertise to let others know that these are to be handled in some special way, unlike those in AS-NIALLNORMAL. According to operational circumstances, there might be periods, even long ones, with nothing special going on; AS-NIALLSPECIAL would then be empty, but only for as long as this continued to be the case. Something I don't know is whether this hypothetical scenario is operationally realistic or simply a product of my certainly ill-informed, and perhaps over-active, imagination. If it were the latter, then a special case just for AS-NULL would be sufficient. Otherwise, inferring equivalence to AS-NULL of any set which happens to have been empty for some specified period seems unsafe. I'll be happy to learn that I'm imagining trouble that can never arise. Niall