I have a question regarding machine learning and specifically kernel functions. Suppose we have a Kernel function, say $K(x)$, and also another distinct one, say $K'(x)$. I want to know is $K(K'(x))$ a kernel function as well? That is, if one feeds the output of a kernel function to another kernel, what does it mean? does it make sense or not?
Another question is about the expected behavior of linear combination of well-known kernels,such as RBF, polynomial and MLP. Suppose the MLP kernel yields 60% of accuracy in a classification task and RBF yields 85%. Does necessarily the RBF+MLP yield a better accuracy compared to the one resulted by MLP?