Most, if not all, of the notions of derivative that I have so far seen have the property that they are locally defined -- meaning that the derivative of a map-type object at a point depends on the map only in an arbitrarily small neighborhood of said point.

One could define some sort of non-local "differential" operator in real analysis for example by convolving a derivative with a function having non-trivial support. I use quotes here, because the operator involves integration as well as differentiation.

A less explicit but more apropos example would be an operator $N$ taking a manifold morphism $\phi$ to a vector bundle morphism $N\phi$, but which does not respect the restriction and gluing concepts used in sheaf theory (which I understand to be an abstract way to say that something is locally defined). The tangent map operator on manifold morphisms is a similar type of object, except that it can be shown to be locally defined. Thus $N\phi$ would "taste" like a derivative in that it has the same form as $T\phi$, but is not locally defined.

- Could an operator such as $N$ qualify as a differential operator (equivalently, would $N\phi$ qualify as a derivative of $\phi$)?
- Generally, what is the essential quality defining a "derivative"? My guess is that an answer would live in the realm of sheaf theory.

pseudo-differential operators, which is usually attached to well-behaved operators in that spirit... $\endgroup$ – Mariano Suárez-Álvarez Jan 30 '12 at 0:164more comments