Per Harv,

"Okay, I understand that set A is the explanandum (that which needs explanation) and the 'elements of A' are the explanans (the individual elements of the explanation that explain the explanandum).

Question 2: What exactly does set B represent in your (revised) model if set A represents the explanandum?"

[b]2. B is a set, defined to be an unordered finite collection of elements of A.[/b]

As I said in my definition, B is an unordered finite collection of elements of A. If you understand what A stands for (that which needs explanation) it should be clear to you what B stands for!

Certainly only a complete idiot would hold that the entirety of A (as it has been defined) is available to us when it comes to comprehending A (or modeling A???): i.e., the presumption that no further information is or ever will be available is a rather provincial position to take even on simple problems (mistakes and misunderstandings happen). On the other hand, the actual information available must contain some part of A: i.e., it must at least contain elements of A or we are wasting our time.

As I say in my essay, "The problem is to create a model which will model any explanation of A obtained from C. As an aside, it should be obvious that the necessity of defining C arises because, if all the elements of A are known, A itself is a model of A and the problem posed is trivial."

Have fun -- Dick