G'morning Aleksej, 

 MM> 3. Each of the 3x3 squares is made up of only one digit from the
 MM> range.

 ARS> I don't understand this. :-(

The 9x9 array of numbers I set out was...

5 0 0  7 0 8  0 0 3
0 0 2  9 3 0  0 0 0
0 0 7  0 6 0  4 1 0

6 0 0  3 0 9  0 5 1
0 1 5  0 0 0  9 2 0
2 7 0  1 0 4  0 0 8

0 4 6  0 1 0  5 0 0
0 0 0  0 9 6  3 0 0
0 0 0  4 0 2  0 0 0

When you've finished solving it,  it looks like this:-

5 9 1  7 4 8  2 6 3
4 6 2  9 3 1  8 7 5
8 3 7  2 6 5  4 1 9

6 8 4  3 2 9  7 5 1
3 1 5  6 8 7  9 2 4
2 7 9  1 5 4  6 3 8

7 4 6  8 1 3  5 9 2
1 2 8  5 9 6  3 4 7
9 5 3  4 7 2  1 8 6

And the numbers 1 - 9 appear only once...

a. In each line,
b. In each column, and
c. In each sub-square of 9 digits.

All very cunning ... with solving it being a matter of careful 
elimination.

Any thoughts on solving these puzzles ?

:-)
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