Markov Inequality Notation Help

Question

I am trying to understand the proof of markov inequality. But I am not familiar with the instructor's notation that published the proof. Here's the photo of the proposition and the proof. What I don't understand is $1{Z /geq}$. It would help a lot if you can clarify what that means. Thanks in advance!

Answer 1

$\mathbf 1\{Z \ge t\}$ is an indicator random variable which takes the values

• $1$ when $Z \ge t$
• $0$ otherwise, so here when $Z \lt t$