Subtraction and divine simplicity

There has been recent interest in subtraction arguments for the thesis that possibly there is nothing concrete. These arguments tend to be based on the thesis that there cannot be a concrete object such that subtracting it necessitates adding something to the world. Here is a much weaker subtraction principle:

1. There is no concrete contingent object o such that there could be a concrete object o* with the property that necessarily o* exists if and only if o does not exist.

This is weaker in several ways than the standard subtraction principle. It only extends to actual objects o. It is restricted to contingent objects. And it rules out only the possibility that there is a single possible concrete o* that, necessarily, exists if and only if o does not.

Now, suppose that divine believings are objects distinct from God. Believings seem to be concrete objects. Let o be God's believing that there are horses and o* be God's believing that there are no horses. Without divine simplicity, o and o* will be distinct from God, and presumably necessarily o* will exist if and only if o does not (since God is necessarily existent and essentially omniscient). But that would violate (1).

So it seems that we shouldn't suppose divine believings to be objects distinct from God. Thus, either divine believings aren't objects, or they are identical with God. In either case, we have divine simplicity with respect to divine believings.