Semantic Web Stack: What does the Proof bit do?

![alt text](upload://bIBCMIotOvCteO3WNgWM1IwNF8I.png)

Yeah, okay, at this stage we all know and love the Semantic Web Stack.

Against my better judgement, I find myself writing about it at the moment in the context of a little historical perspective for the Semantic Web.

But I'm stuck on the Proof bit. What was the original idea behind the Proof layer? My gut tells me that it was to do with the "oh yeah?" button that would be able to "prove" conclusions made by reasoners and so forth, but I've not been able to find anything concrete on the matter and Proof could well mean a lot of things.

Anyone have pointers to some material (or thoughts) about what the Proof layer is doing in there?

Maybe someone has seen the Proof layer lying about somewhere?

Here is what TimBL has said about this in an old design issues document:

From what I read here and from what I think to remember from other statements that I heard/read, the idea was probably to use formal proofs in fully-automatic agent-based negotiation or access-request activities, where one client agent (on behalf of a human) proofs to some service agent that it is allowed to access some information, etc. So there would probably be some client-specific challenge, stated in the form of an assertion in logic (see the layer below), and the client agent would have to provide a formal proof for it, otherwise (for other clients without access), creating such a proof would be too hard computationally. As checking a proof is much easier than creating it (without clues), the service agent would be able to check whether the client agent has access rights or not (or whatever). Based on all of this is then - obviously - trust! :-)

Now, this all sounds a little odd today, and I haven't heard of such a logic/proof based method for access control in the last years, and this may mean that the proof part is perhaps not relevant anymore.

PS: I believe to remember that the classic Scientific American article as of 2001 included something about this agent-related stuff. EDIT: Signified's self-response provides a proof! :-)