Knights of the Square Sudoku Table

 8  .  . | .  .  . | .  .  6 
 .  .  4 | .  .  . | .  .  . 
 .  .  . | .  .  . | 9  1  . 
---------+---------+--------
 .  .  . | .  2  . | .  .  . 
 .  .  9 | 3  .  . | .  .  . 
 .  .  . | .  .  . | .  .  . 
---------+---------+--------
 .  .  . | 9  .  7 | .  .  . 
 9  .  . | 6  3  . | 4  .  . 
 .  .  . | .  .  . | 1  .  . 

• Normal sudoku rules apply.
• Long diagonals contain only unique values.
• If A is a box-center, and A and B are a knight’s move apart, then A and B ought to be different.

A knight’s move constitutes going up/down by two followed by going left/right by one, or going up/down by one followed by going left/right by two:

. . B . B . .
. B . . . B .
. . . A . . .
. B . . . B .
. . B . B . .