Specifically, In order to prove the formula (20), we have to find an expression for the (k) that gives to g the correct contribution to the formula: First, we observe that g does not appear in the terms that contain the intersection of more than k sentences.
specifically, (t) is not affected by g if t ≥ k. g is affected by all the (t) for which t ≤ k. Given that g appears in the sentences {s i 1 , .