Mutually Orthogonal Latin order 10

 A predecessor to Sudoku:

Emi Kasai bases on a Mutually Orthogonal Latin squares (MOLS)

https://en.wikipedia.org/wiki/Mutually_orthogonal_Latin_squares#Euler's_conjecture_and_disproof

http://martin-gardner.org/SciAm12.html

Devwebcl's Madness

 Inspired by Scientific American's article.