Up onBy the Schwartz kernel theoremKernel Theorem, we know that the kernel of an integral operator belongs to distribution space S'(R^n)$\mathscr{S}'(\mathbb{R}^n)$. Moreover, we know that the kernel K$K$ is $C^{\infty}$ off the diagonal in $\mathbb{R}^n \times \mathbb{R}^n$.
Now my questions are that
1- Does the Schwartz kernel of pseudo-differential operator of arbitrary order belong to Schwartz space?:
2- Can we have the Schwartz kernel Theorem with kernel belong to S(R^n) Not S'(R^n)?
Does the Schwartz kernel of a pseudo-differential operator of arbitrary order belong to the Schwartz space?
Can we have the Schwartz Kernel Theorem be true with the kernel belonging to $\mathscr{S}(\mathbb{R}^n)$ as opposed to $\mathscr{S}'(\mathbb{R}^n)$?