Replace inner kernel for pickling
Motivation: When I want to enable pickling of symbolic expression in Pytential (pytential!133 (merged)), replace_inner_kernel
is undefined at this line.
I think the intention here is to move the derivative inside the inner kernel, but I'm not sure whether my implementation is sensible or correct.
cc @inducer
To-do: Review !133 (merged) when this is in.
Edited by Andreas Klöckner