group() {
	surface(file = "surface-simple.dat", center = true, invert = false);
	multmatrix([[1, 0, 0, 2], [0, 1, 0, 0], [0, 0, 1, 0], [0, 0, 0, 1]]) {
		surface(file = "surface-simple2.dat", center = true, invert = false);
	}
}
