Abstract
We consider means of the form u = 3 root f is variables, and we show that if it n <= 4 and u is internal on the points (x(i), ... , x(n)) where,x(i) = 0 or 1, then mu is internal for all points (x(1) ... , x(n)) with x(i) >= 0 for all i. We highlight the similarity between this internality problem and the parallel problem pertaining to copositive symmetric cubic forms.