Graeco-Latin squares

Let $A=(a_{ij})$ and $B=(b_{ij})$ be two $n\times n$ matrices. We define their as the matrix whose $(i,j)$ th entry is the pair $(a_{ij},b_{ij})$ .

The name comes from Euler’s use of Greek and Latin letters to differentiate the entries on each array.

An example of Graeco-Latin square:

\begin{pmatrix}a\alpha&b\beta&c\gamma&d\delta\\ d\gamma&c\delta&b\alpha&a\beta\\ b\delta&a\gamma&d\beta&c\alpha\\ c\beta&d\alpha&a\delta&b\gamma\end{pmatrix}