First, note that (2) implies that: Note that P({ω : f ∈ ω}|y i ) involves the sum of weights over all x ∈ X subject to the conditions that N (x) = 1 and α f (x) = 1.
p({ω : f ∈ ω}|y i ) can also be expressed in a form that is easy to evaluate using graphical techniques.