Inyuki, 
Negative Cardinality
A mathematical set property of having less than 0 elements (Just like antimatter in Physics.)
The invention of negative numbers proved to be useful in mathematics. Set operations, however, do not have the idea of having less than 0 elements. We reach the empty set {}, and then stop, but why should we? Imagine a property: subtracting an element that is not in a set creates a potentiality to annihilate such element. Such potentiality could be marked as elements with an apostrophe. I.e., {1,2',2} = {1}.
This idea was inspired by "World’s Most Exclusive Club," when thinking about the super-exclusiveness.
Credits: Inyuki of HalfBakery.
Brining sets with quantifiabiable cardinality into common use in mathematics.
Goals are just assets with negative sign of carnality, so such theory would be useful for formalizing goal pursuit...
Yeah, perhaps it could simplify accounting, or maybe, it could even help make goal-pursuit more imaginary, as everything that's formalized as a set of sets of ... of sets, could suddenly have that imaginary component ("goals are just imaginary assets").
Negative cardinality is deficit of something, a task yet to be done. It has to do with sequence, then, and time. Really interesting