Sorry, it is corollary to: Any two norms on a finite-dimensional linear space are equivalent.
Definition: Let X and Y be metric spaces. An operator \(\displaystyle f:X\rightarrow Y\) is said to be continuous at a point \(\displaystyle a\in X\) if, for every \(\displaystyle \epsilon >0\), there exists a \(\displaystyle \delta >0\) such that:
\[ \varrho(x,a)< \delta \Rightarrow \varrho(f(x), f(a))< \epsilon\]
