The eight queens puzzle is the problem of placing eight chess queens on an 8x8 chessboard
so that no two queens threaten each other.

Thus, a solution requires that no two queens share the same row, column, or diagonal.

The eight queens puzzle is an example of the more general n-queens problem of placing n queens on an nxn chessboard,
where solutions exist for all natural numbers n with the exception of n=2 or n=3.

( from:
http://en.wikipedia.org/wiki/Eight_queens_puzzle
)

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