Plateaudness of Kasami APN functions

It is shown that the Kasami function defined on ${\mathbb{F}}_{2^n}$ with n even is plateaued. This generalizes a result [3, Theorem 11], where the restriction $(n,3)=1$ is assumed. The result is used to establish the CCZ-inequivalence of the Kasami function defined on ${\mathbb{F}}_{2^n}$ with n even to the other known monomial APN functions [4].