Math-Geek Challenge

[furrbear]

∀ε>0 ∃δ>0 ∋ 0<|x-a|<δ⇒|ƒ(x)-L|<ε

Answer: Karl Weierstrass' Formal Definition of a Limit:

Let f be a real-valued function defined on an open interval of real numbers containing c (except possibly at c) and let L be a real number. Then

means that

for each real ε > 0 there exists a real δ > 0 such that for all x with 0 < |x − c| < δ, we have |f(x) − L| < ε.

or, symbolically,

fzks_cub was the first to respond with the words "definition of the limit"

Those who answered jrjarrett got the location from where I saw it correct, but missed the correct answer.