Latin square

A Latin square of $n$ is an $n\times n$ array such that each column and each row are made with the same $n$ symbols, using every one exactly once .

Examples.

\left(\begin{array}[]{cccc}a&b&c&d\\ c&d&a&b\\ d&c&b&a\\ b&a&d&c\end{array}\right)\qquad\left(\begin{array}[]{cccc}1&2&3&4\\ 4&3&2&1\\ 2&1&4&3\\ 3&4&1&2\end{array}\right)