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Jul 17, 2023 at 2:50 comment added Andreas Haupt One more request for a pointer: I am seeking to generalize the above argument to general random walks (i.e. non-Rademacher increments). What is a good text on reflection principle and probability of staying positive for a general random walk?
Aug 24, 2021 at 16:20 vote accept Andreas Haupt
Aug 24, 2021 at 15:44 comment added fedja @AndreasHaupt Sure: $P(S<B)\le\sum_{s=0^B}P(X_{T-s}=0)$, for example. As to the square root, the standard application of the reflection principle for the simple random walk yields that $P(S_1,S_2,\dots,S_{2n}>0)=2^{-2n}{2n-1\choose n-1}$ and Stirling finishes the story.
Aug 24, 2021 at 14:28 comment added Andreas Haupt Thank you @fedja, this has been very helpful! Could you expand a bit why the probability of being in a particular position tending to zero implies that $S$ is large? Also, do you have a reference on the square-root statement?
Aug 24, 2021 at 1:29 history answered fedja CC BY-SA 4.0