Completing Latin Squares

Using only the numbers 1, 2, 3, and 4, arrange four sets of these numbers into a four-by-four array so that no column or row contains the same two numbers. The result is known as a Latin square.

Here are two examples of Latin squares of order 4:

1	2	3	4
2	1	4	3
3	4	1	2
4	3	2	1

1	2	3	4
3	4	1	2
4	3	2	1
2	1	4	3

In effect, each row (and each column) is a permutation of four distinct numbers (or symbols).