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Feb 21 at 20:39 comment added Rob Arthan @IosifPinelis: sure! thanks for all your time on what turned out to be a diversion which turned out not to be relevant to my current problem but may perhaps help others.
Feb 21 at 16:31 comment added Iosif Pinelis You also had $\lambda$ going to $0$, rather than $\infty$. So, whatever the value of the original or changed question may be, the post should not be deleted.
Feb 21 at 16:10 comment added Rob Arthan Apologies, there was a repeated and highly significant typo in the above: "${} < \lambda$" should read "${} > \lambda$" throughout. What we were looking for is an upper bound, tending to $0$ as $\lambda \to \infty$ on $P[\max_{1\le j < k \le n}[|S_k - S_j| > \lambda]$. That turns out to be easier to find that we thought at first (using the Kolmogorov and triangle inequalities), so I am happy with the answer given below, as it resolves the original (unintended) question.
Feb 21 at 14:22 comment added Iosif Pinelis You should not change the question, especially so drastically, especially after an answer was given (which you gratefully accepted).
Feb 21 at 13:52 history edited Rob Arthan CC BY-SA 4.0
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Feb 21 at 13:50 comment added Rob Arthan In fact, I think the amended question actually follows easily from the Kolmogorov inequality and the triangle inequality. So I think I'lll delete this question as I don't think it adds much value to MO users.
Feb 21 at 13:32 history edited Rob Arthan CC BY-SA 4.0
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Feb 21 at 13:13 history edited Rob Arthan CC BY-SA 4.0
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Feb 21 at 13:08 history edited Rob Arthan CC BY-SA 4.0
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Feb 19 at 20:55 comment added Rob Arthan @IosifPinelis: I have changed the notation in the question.
Feb 19 at 20:55 history edited Rob Arthan CC BY-SA 4.0
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Feb 19 at 20:52 comment added Iosif Pinelis It is not a good idea to use $\Bbb P$ and $\Bbb E$ to denote the probability and the expectation; use $P,E$ or $\mathsf P,\mathsf E$ instead. Blackboard bold is reserved for $\Bbb R$, $\Bbb C$, $\Bbb Z$, and other similar sets.
Feb 19 at 20:51 vote accept Rob Arthan
Feb 19 at 20:48 comment added Iosif Pinelis Kolmorogov's maximal inequality provides a lower bound on $P(\max_{1\le k \le n}|S_k| < \lambda)$.
Feb 19 at 20:47 answer added Iosif Pinelis timeline score: 1
Feb 19 at 20:27 history asked Rob Arthan CC BY-SA 4.0