Correct invariant for NamingSystem (nsd-1). Two issues here. First, uniqueId is a collection, so you cannot compare it directly to 'uuid'. Second, text says: "Root systems cannot have uuid identifiers", but the expression "reads kind != 'root' or uniqueId.type = 'uuid'", which means the opposite.

The correct version probably should be:

kind = 'root' implies uniqueId.all(type != 'uuid')