TITLE: Reading equations: Upside down A
QUESTION [8 upvotes]: what does this equation mean? I´m really bad in reading those, so if somebody explained it, I would really appreciate.

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

REPLY [14 votes]: The symbol "$\forall$" means "for all" or "for every".
"$\forall i \in \lbrace 0,1,2 \rbrace$" means
"for all $i$ in the set $\lbrace 0,1,2 \rbrace$".