Solution
= Solution
A <sequence> $(x_n)$ in a <metric space> $(X,d)$ is a <Cauchy sequence> if
$$
\forall\varepsilon>0\ \exists N\ \forall m,n\geq N:\quad d(x_m,x_n)<\varepsilon.
$$
The index $N$ may depend on $\varepsilon$, but must work for every pair of sufficiently late terms. No candidate limit is part of this definition.