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I believe the question here makes assumptions which invalidate the endeavor. You assume that "nothing" is something which exists; without getting into the philosophical and formal approaches to the concept of "nothingness," this is patently contradictory.

Taking from the discussion here, one may propose that "nothing" can be defined as "not anything," or in a very rough sense, the negation of all that there is (minus the contradictory negating of course; refer to the history of modern set theories and formal logic to see what I mean).

So, in the strictest sense, it is not possible to subtract not anything from any set as subtraction is a binary operation; i.e., what you are asking equivalent to asking, for example, "58 - ". Doesn't hold, does it?

At any rate, I hope I've addressed your concern here.