IDP NQueens Problem

Put 8 queens on the chess board so that none of the queens can attack each other (horizontally, vertically or diagonally). You can use the following vocabulary:

vocabulary V {
    type index isa int
    queen(index, index)
    n : index
    type diag isa int
    diag1(index, index) : diag
    diag2(index, index) : diag
}