How to show if $cos^n(x^2-y^2)$ is a valid mercer kernel function if $n$ is positive?
For $cos(x^2-y^2)$ I would assume that: $cos(x^2-y^2) = sin(x^2)sin(y^2)+cos(x^2)cos(y^2)$ Is a valid mercer kernel with feature map $\phi(x) = (cos(x^2), sin(x^2))^T$