graphoids

A form of graphoid — A matroid that has two collections of nonempty subsets called circuits and cocircuits such that the intersection of any circuit and cocircuit is not only the identity matroid, no circuit properly contains another circuit, no cocircuit properly contains another cocircuit, and for any painting of M that colors exactly one element green and the rest either red or blue there exists either a circuit containing the green element and no red elements or a cocircuit containing the green element and no blue elements.