Credential Surfaces

[bblfish]

Trying to map the JsonLD Verifiable Credentials Data Model to N3, I came across what is clearly a rdf surfaces-related problem which I detailed in issue 1248 of the VC repo. So I thought I'd bring this to the group's attention here as this is a very clear use case for what we were discussing as neither positive nor negative surfaces but simply containers of triples surfaces...

The surface aspect of VC is made clear by figure 6 of §3.2 Credentials reproduced below.

It relates graphs on colo§red surfaces, which are essential to our understanding of credentials.
It also raises an interesting question for N3 too: how can write arrows pointing at such nodes inside of graphs?

As shown in the diagram, a VC is data about a claim. The claim on the Yellow surface to the right should not initially be taken as true or false by a Guard. If the signature on the green surface is verified, then the top surface in pink can be seen to be true. Whether the yellow surface is then believed depends on how much one trusts the issuer.
In this case the University is making a claim about one of its members, so that seems like a reasonable claim to trust it to make.

This is a clear use case or application of the says modal logic,