Hi, I need to demonstrate that U(x) = phi(x) + x*Phi(x) > 0 for all x. This is clearly true for x >= 0. In addition U'(x) > 0 for all x, and thus it is a strictly increasing function. It would be sufficient to show, for instance that lim (x-> - infinity) U(x) = 0 Any suggestion ? Thanks in advance, Esteban You may leave the list at any time by sending the command SIGNOFF allstat to [log in to unmask], leaving the subject line blank.