domain NQueens
{
    primitive Size  ::= (m: Natural).
    primitive Queen ::= (x: Natural, y: Natural).

    WrongNumberOfQueens := Size(m), count(Queen(_,_)) != m.

    NumberTooBig := Queen(x,_), Size(m), x >= m .
    NumberTooBig := c is Queen, s is Size, c.y >= s.m .

    SameRow      := a is Queen, b is Queen, a.y = b.y, a != b.    
    SameColumn   := a is Queen, b is Queen, a.x = b.x, a != b.
    SameDiagonal := a is Queen, b is Queen, a != b, a.x - a.y = b.x - b.y.
    SameDiagonal := a is Queen, b is Queen, a != b, a.x + a.y = b.x + b.y.

    conforms := !WrongNumberOfQueens & !NumberTooBig & !SameRow & !SameColumn & !SameDiagonal.
}

partial model Queens16 of NQueens
{
    Size(16)    
    Queen( 0,_) Queen( 1,_) Queen( 2,_) Queen( 3,_) Queen( 4,_)
    Queen( 5,_) Queen( 6,_) Queen( 7,_) Queen( 8,_) Queen( 9,_)
    Queen(10,_) Queen(11,_) Queen(12,_) Queen(13,_) Queen(14,_)
    Queen(15,_)
}