Let $f \colon X \to X$ be a reversible dynamical system on a compact metric space. A $\delta$-chain is a sequence $(x_k)$, $k \in \mathbb{Z}$ such that
$$d\big(f(x_k), x_{k+1}\big) \le \delta, \qquad \forall , k \in \mathbb{Z}.$$
A point $y \in X$ is said to $\varepsilon$-shadow a the $\delta$-chain $(x_k)$ if
$$d\big(f^k(y), x_k\big) \le \varepsilon, \qquad \forall , k \in \mathbb{Z}.$$
Today we prove the Shadowing Theorem, which roughly speaking asserts that in the presence of hyperbolicity, for any $\varepsilon>0$ there exists $\delta >0$ such that every $\delta$-chain is $\varepsilon$-shadowed by exactly one point.