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Smooth manifolds and smooth functions between them. For manifolds with additional structure, see more specific tags, such as [riemannian-geometry]. For more topological aspects, see [differential-topology].

5 votes
1 answer
335 views

Sufficient conditions for $\mathrm{Der}_k(A)$ to be f.g. projective

Let $k$ be a field and $A$ a commutative $k$-algebra. What are sufficient conditions for the module of derivations $\mathrm{Der}_k(A)$ to be finitely generated projective? I'm looking for conditions w …
Tobias Fritz's user avatar
  • 6,406
9 votes

Is the class of n-dimensional manifolds essentially small?

Already in dimension $0$, the collection of all manifolds in the sense of the OP is a proper class: any set, equipped with the discrete topology, is a $0$-dimensional manifold. In dimension $n$, one c …
Tobias Fritz's user avatar
  • 6,406
12 votes
1 answer
408 views

Are algebras of smooth functions formally smooth?

Let $M$ be a manifold. Then is the ring of smooth functions $C^\infty(M,\mathbb{R})$ formally smooth over $\mathbb{R}$? If it helps, feel free to assume that $M$ is compact. (This is not a joke quest …
Tobias Fritz's user avatar
  • 6,406
17 votes

Do rings of smooth functions differ from rings of continuous functions?

Another conceptually interesting way to see that the answer is negative is to make the following observations (related to Tom Goodwillie's answer): For any topological space $X$, the algebra of real- …
Tobias Fritz's user avatar
  • 6,406