In a game of chess, a queen is able to move any number of squares in an orthogonal direction (up, down, left or right) or diagonally and can capture any piece that blocks its line of movement.
What is the largest number of peaceful queens you can place on a 4x4 chessboard, so that no queen threatens any other queen?
It is possible to place four peaceful queens on a 4x4 grid.
How many peaceful queens can you place on a standard 8x8 chessboard?
What about other pieces, like a castle (rook), a bishop or a knight?