Euclidean Metric

The Function $f:\Bbb{R}^n\times \Bbb{R}^n\to\Bbb{R}$ that assigns to any two Vectors ($x_1$, ..., $x_n$) and ($y_1$, ..., $y_n$) the number

$$\sqrt{ (x_1 - y_1)^2 + \ldots + (x_n - y_n)^2},$$

and so gives the ``standard'' distance between any two Vectors in $\Bbb{R}^n$.