David Williams Probability With Martingales Solutions Best -

But the best solution here is not the example — it’s the insight : strict inequality means some probability mass is lost in the limit because ( M_n ) is not uniformly integrable. Williams wants you to feel the difference between a.s. convergence and ( L^1 ) convergence.

These are the foundations. If you can't solve these without help, you likely need to re-read the preceding chapter. david williams probability with martingales solutions best

Her instinct was to expand and condition blindly. She wrote pages of algebra, got lost, and peeked at the back—where Williams often writes not a full solution, but a mocking or encouraging remark. For this exercise? “Use the ‘increment trick’ and the fact that ( X_n^2 - n ) is a martingale.” But the best solution here is not the