+typedef Stats<false> History;
+typedef Stats<true> Gains;
+
+
+/// MovePicker class is used to pick one pseudo legal move at a time from the
+/// current position. The most important method is next_move(), which returns a
+/// new pseudo legal move each time it is called, until there are no moves left,
+/// when MOVE_NONE is returned. In order to improve the efficiency of the alpha
+/// beta algorithm, MovePicker attempts to return the moves which are most likely
+/// to get a cut-off first.