[unimpressive]

>I think the crucial layer that we need to implement... a lot of things... is a global immutable (aka referentially transparent) namespace.

Theodore Nelson has said this himself, I can't remember the exact source but I think it was in his google talk he said that you need permanent addressing for Xanadu to work. He at least reiterates the concept (though with less principal importance) here:

http://xanadu.com/XanaduSpace/btf.htm

"STABILIZED ADDRESSES

Imagine that everything you type is given a permanent, immutable address. Then to refer to a given sentence, or paragraph, you would refer to its permanent address span (start, length). This would have many benefits.

This is not the way things are ordinarily done, but in this system we simulate such permanent addresses in order to get these benefits."