probability - Condition for strong law of large numbers

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 - Wikipedia

PDF) Conditional strong law of large number

Get Answer) - Exercise 3.4 Use The Steps Below To Prove A Version Of The Strong

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PDF) On the strong law of large numbers for φ-mixing and ρ-mixing random variables

PDF) Generalization of strong law of large numbers for nonnegative random variables

Proof of the Law of Large Numbers Part 2: The Strong Law, by Andrew Rothman

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13. The Weak Law and the Strong Law of Large Numbers - ppt video online download

Probability theory - Statistics, Random Variables, Law