  Finally, we might accept VD and VR, but deny that our construction of an observable f(Q) is unambiguous. Thus, though f(Q) and g(P) are mathematically identical, we could assume that they correspond to different observables, arguing that an actual determination of v(f(Q)) must proceed via measuring Q, but the determination of v(g(P)) involves measuring P which is incompatible with Q. Since v(f(Q)) and v(g(P)) are thus outcomes of different measurement situations, there is no reason to assume that v(f(Q)) = v(g(P)). This way to block the KS proof comes to understanding f(Q) and g(P) as different observables (because of sensitivity to context), thus it amounts to rejecting NC. There are mainly two ways, in the literature, to further motivate this step. Accordingly, there are two important brands of contextuality to be discussed — causal and ontological contextuality.