param n integer = 8;

var Row {1..n} integer >= 1 <= n;
   # Row[j] is the row where column j's queen is placed

subj to c1: alldiff ({j in 1..n} Row[j]);
subj to c2: alldiff ({j in 1..n} Row[j]+j);
subj to c3: alldiff ({j in 1..n} Row[j]-j);