c130.
Nives Dolšak and Elinor Ostrom, “The Challenges of the Commons”, in Nives Dolšak and Elinor Ostrom, eds. (2003), The Commons in the New Millennium. The definition of subtractivity in the first sentence is a quotation from this source. It is not quite the same as a zero-sum game, where the total reward is constant; subtractivity is about changing shares of a total reward which may increase (or decline).