[curtisblaine]

I don't understand why I can't place two kings in "adjacent diagonal" position when they're in two different regions. Something like:

..k..

.k...

Rules state they must be in different regions, row and column. No mention of diagonal or adjacency.

[codebje]

Maybe it wasn't there when you played, but rule 6 states kings cannot attack each other; chess kings can move one square in any direction. Without this rule the puzzle isn't solvable by logic, only trial and error.

[deepakrb]

Ah this rule is mentioned under “Kings cannot attack each other” (in the chess sense, two Kings cannot be diagonal from one another). I’ve updated the rule to make this a little clearer

[billforsternz]

I agree, I had the same problem.