Poor Jamie Oliver. He spent months battling Miss ­Trunchbull-like dinner ­ladies trying to get them to serve rocket salad rather than chips. But ­according to Cornell ­University researchers Brian Wansink and David R Just, who did a series of experiments in US schools, all he had to do was to shift the goalposts. And the salad bar. By using supermarket-style ­behavioural ­psychology tricks such as moving the salad bar away from the wall and ­renaming corn as, er, "creamy corn", sales of some healthy foods ­tripled in canteens. Child obesity solved. Next!