group() {
	difference() {
		square(size = [10, 10], center = true);
#		circle($fn = 0, $fa = 12, $fs = 2, r = 3);
	}
#	group() {
		square(size = [11, 12], center = false);
	}
#	multmatrix([[1, 0, 0, 0], [0, 1, 0, -12], [0, 0, 1, 0], [0, 0, 0, 1]]) {
		difference() {
			square(size = [10, 10], center = true);
			square(size = [5, 5], center = true);
		}
	}
}
