i33 = [1, 0, 0; 0, 1, 0; 0, 0, 1];
i23 = [1, 0, 0; 0, 1, 0];
(eye (3) == i33 && eye (size (i33)) == i33 && eye (3, 3) == i33
 && eye (2, 3) == i23 && eye (3, 2) == i23')
