group() {
	multmatrix([[1, 0, 0, -20], [0, 1, 0, 30], [0, 0, 1, 0], [0, 0, 0, 1]]) {
		group() {
			minkowski(convexity = 0) {
				difference() {
					cube(size = [10, 10, 5], center = true);
					cube(size = [8, 8, 10], center = true);
				}
				cylinder($fn = 0, $fa = 12, $fs = 2, h = 1, r1 = 2, r2 = 2, center = false);
			}
		}
	}
	multmatrix([[1, 0, 0, 0], [0, 1, 0, 25], [0, 0, 1, 0], [0, 0, 0, 1]]) {
		group() {
			minkowski(convexity = 0) {
				difference() {
					cube(size = [10, 10, 5], center = false);
					cube(size = [5, 5, 5], center = false);
				}
				cylinder($fn = 0, $fa = 12, $fs = 2, h = 5, r1 = 5, r2 = 5, center = false);
			}
		}
	}
	multmatrix([[1, 0, 0, 25], [0, 1, 0, 25], [0, 0, 1, 0], [0, 0, 0, 1]]) {
		group() {
			minkowski(convexity = 0) {
				cube(size = [10, 10, 5], center = false);
				cylinder($fn = 0, $fa = 12, $fs = 2, h = 5, r1 = 5, r2 = 5, center = false);
			}
		}
	}
	multmatrix([[1, 0, 0, 0], [0, 1, 0, 0], [0, 0, 1, 0], [0, 0, 0, 1]]) {
		minkowski(convexity = 0) {
			cube(size = [10, 10, 5], center = false);
		}
	}
	minkowski(convexity = 0);
	minkowski(convexity = 0);
}