assert(piece_on(to)==piece_of_color_and_type(us, promotion));
assert(promotion >= KNIGHT && promotion <= QUEEN);
clear_bit(&(byColorBB[us]), to);
assert(piece_on(to)==piece_of_color_and_type(us, promotion));
assert(promotion >= KNIGHT && promotion <= QUEEN);
clear_bit(&(byColorBB[us]), to);