vex function \\( \\|x - z\\|^2 \\) over \\( z \\in D \\). Using the first-order optimality condition for convex functions on convex sets, we obtain \\( (\\mathrm{proj}_D(x) - x)^T(y - \\mathrm{proj}_D(x)) \\geq 0 \\), for all \\( y \\in D \\).";
                    case 8:
                        return "The text shows that the Hessian of the least-squares objective function is \\( 2A^TA \\), which is positive definite when \\( A \\) has full column rank. Therefore, the least-squares objective function is s