Math — Limits (Epsilon–Delta)

\forall \varepsilon > 0,\ \exists\, \delta > 0

0 < |x - a| < \delta \Rightarrow |f(x) - L| < \varepsilon

\lim_{x\to a} f(x) = L

\text{Cauchy: } |a_m - a_n| < \varepsilon