math problem

 

Each unit square of the 4x4 grid below is to be filled in with the number 1, 2, 3 or 4, so that:  

Each row contains the numbers 1, 2, 3, and 4 in some order,  

Each column contains the numbers 1, 2, 3, and 4 in some order, and   

Each  square (outlined in bold) contains the numbers 1, 2, 3, and 4.  

 

 

I can't see the grid.  But you can do this by just   

rotating the sequence of the numbers one over.  

 

Like this:   

 

                                   1   2   3   4   

                                   2   3   4   1   

                                   3   4   1   2   

                                   4   1   2   3   

_.