probability - Condition for strong law of large numbers : Understanding the solution - Mathematics Stack Exchange

I am reading the solution of the following task: Here is the solution: From where does the last inequality in the second line comes from? Everything else is totally clear to me.

Law of Large Numbers - Definition, Examples, Insurance, Statistics

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Mathematics: Its Content, Methods and Meaning (3 Volumes in One): Aleksandrov, A. D., Kolmogorov, A. N., Lavrent'ev, M. A.: 9780486409160: : Books

Solved The Strong Law of Large Numbers states that Xˉ→E[X]

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probability theory - In the Proof of Kolmogorov's Strong Law of Large Numbers - Mathematics Stack Exchange

Laws of Large Numbers (detailed explanation), by Anirudh G

Law of Large Numbers Strong and weak, with proofs and exercises

Law of Large Numbers Strong and weak, with proofs and exercises

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