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what does this equation mean? I´m really bad in reading those, so if somebody explained it, I would really appreciate.

$f_i(x,y)\ge 0\quad\forall i\{0,1,2\}$

Asaf Karagila
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dan
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    Personal pet peeve: It is not an equation. An equation is a statement that two things are equal (has an equals sign). Your question involves the statement that $f_i(x,y)\geq0$ if $i$ is 0,1, 2. – MJoszef Jan 19 '12 at 16:12
  • totally agree, my bad. – dan Jan 19 '12 at 16:30

1 Answers1

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The symbol "$\forall$" means "for all" or "for every".

"$\forall i \in \lbrace 0,1,2 \rbrace$" means "for all $i$ in the set $\lbrace 0,1,2 \rbrace$".

David Mitra
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  • thank you. It means i can only be 0,1,2 am I right, and nothing more basically? – dan Jan 19 '12 at 15:26
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    @dan: It means that the statement is true for each of these three values of $i$: $f_0(x,y)\ge 0$, $f_1(x,y)\ge 0$, and $f_2(x,y)\ge 0$. It says nothing about $f_i(x,y)$ if $i$ is not $0,1$, or $2$. – Brian M. Scott Jan 19 '12 at 15:28
  • Why can't I get "{" and "}" to render (I've used them before here)? "\lbrace" and "\rbrace" work fine... – David Mitra Jan 19 '12 at 15:30
  • ok I get it now, thanks to all of you guys! – dan Jan 19 '12 at 15:32
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    And is there a prounounciation for it or if I see ∀α.r should I read that as "for all alpha dot r"? – gman Feb 07 '16 at 08:50