Question

I’m solving the classical eight queens problem in prolog. And now I’m about to start coding the bit that removes reflections about the horizontal line. Y=4. Say if the point (3.3) is reflected, the new point would be (6,6), is that correct? Another example, (2,1) would become (7,8).

Answer 1

The ones you show are not reflections but rotations.

• The reflection along the vertical center-axis (flip left-right) of a square (x,y) is given by (9-x,y) (assuming 1<=x,y<=8).

• The reflection along the horizontal center-axis (flip top-bottom) is given by (x,9-y).

• The reflection by both axes (aka rotation) is given by (9-x,9-y)