But while statement 2 overcomes the problem of worlds at which there is some extra stuff (sometimes referred to as the "epiphenomenal ectoplasm problem") it faces a different challenge: the so-called "blockers problem". Imagine a world where the relation between the physical and non-physical properties at this world (call the world "w1") is slightly weaker than metaphysical necessitation, such that a certain kind of non-physical intervener—"a blocker"—could, were it to exist at "w1," prevent the non-physical properties in "w1" from being instantiated by the instantiation of the physical properties at "w1." Since statement 2 rules out worlds which are physical duplicates of "w1" that also contain non-physical interveners by virtue of the minimality, or that's-all clause, statement 2 gives the (allegedly) incorrect result that physicalism is true at "w1." One response to this problem is to abandon statement 2 in favour of the alternative possibility mentioned earlier in which supervenience-based formulations of physicalism are restricted to what David Chalmers (1996) calls "positive properties". A positive property is one that "...if instantiated in a world W, is also instantiated by the corresponding individual in all worlds that contain W as a proper part." Following this suggestion, we can then formulate physicalism as follows: