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Following is an equation (taken from Reinforcement Learning field). How can I add the first sign (like 1) in LaTeX and what does it mean?

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Phelype Oleinik
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Avi
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  • also related https://tex.stackexchange.com/questions/26637/how-do-you-get-mathbb1-to-work-characteristic-function-of-a-set – Marijn Sep 17 '19 at 17:03
  • Thanks! What is the official name of the function? – Avi Sep 17 '19 at 17:11
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    The font style is called Blackboard bold or double struck, see https://en.wikipedia.org/wiki/Blackboard_bold. From that page about the : "Often represents, in set theory, the top element of a forcing poset, or occasionally the identity matrix in a matrix ring. Also used for the indicator function and the unit step function, and for the identity operator or identity matrix." The linked question calls it "characteristic function of a set". – Marijn Sep 17 '19 at 17:53

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