S9 LIB  (queens n)  ==>  list

Solve the N-Queens puzzle using AMK. All solutions for the
given board size will be returned, where the offset in each
list is an X position on the board and the value at that
offset is the corresponding Y position. E.g., the board
(2 0 3 1) would look like this:

. . & . 3
& . . . 2
. . . & 1
. & . . 0
0 1 2 3

(queens 4)  ==>  ((2 0 3 1) (1 3 0 2))
