Continuous

Let $X \subset \mathbb{R}$ and let $t \in X%. We say that a function $f \colon X \rightarrow \mathbb{R}$ is continuous at $t$ if for every $\epsilon >0$ there exists $\delta >0$ so that for all $s \in (t-\delta,t+\delta) \bigcap X$, $|f(t)-f(s)|<\epsilon$.