. .  4 2
2 .  . 3

. .  . .
. .  3 1
==
Solution
3 1  4 2
2 4  1 3

1 3  2 4
4 2  3 1
==
Create
Regexp::Sudoku:: -> new -> init (size => 4) -> set_cross
==
Name: Default diagonals, 4 x 4 (Griddlers 25374)
URL: https://www.griddlers.net/sudoku/-/sudoku/25374