$ N-queens problem
$
$ Place n queens on an nxn chess board 
$ without attacking each other.
$
ESSENCE' 1.0
given n : int
letting         AMOUNT_QUEENS be domain int(0..n-1)
find            queens : matrix indexed by [ AMOUNT_QUEENS ] of AMOUNT_QUEENS

such that       alldifferent(queens),	    
                forall i,j : AMOUNT_QUEENS . 
                   (i > j) =>
                         ((queens[i] - i != queens[j] - j)
                      /\ (queens[i] + i != queens[j] + j))