Discrete thinking - Play & Observe!
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you can move numbers in any quadrant at the following positions to [x][y]:
[x][y] or // upper left quadrant [x][2*n-1-y] or // upper right quadrant [2*n-1-x][y], or // lower left quadrant [2*n-1-x][2*n-1-y] // lower right quadrant
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