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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].

11 votes
Accepted

On the $\mathbb R$-algebra structure on $C^\infty(M)$.

If $M$ is connected then one can determine $\mathbb{R}$ (the constant functions) within $C^\infty(M)$ (the ring of smooth real-valued functions on $M$). One can certainly determine $\mathbb{Q}$ withi …
Robin Chapman's user avatar
9 votes
Accepted

The ring $C^{\infty}(M)$?

You are correct: $C^\infty(M)$ does contain all the geometry and topology of $M$ (at least when it is considered as an $\mathbb{R}$-algebra). For example when $M$ is compact the points of $M$ correspo …
Robin Chapman's user avatar
5 votes

Which manifolds admit a diffeomorphism of order $n$?

Here's an example with $g=2$ and $n=5$. Consider the hyperelliptic curve defined by the equation $$y^2=x^5-1$$ or to be more precise the corresponding desingularized projective curve. Now this is a Ri …
Robin Chapman's user avatar
4 votes
Accepted

Ideals in the ring of smooth endomorphisms of the real line

This is all fairly well-known stuff. In Q1, the ideal $I_p^n$ is the set of functions for which the derivatives up to order $n-1$ at $p$ vanish in a local coordinate system centred at $p$. I'll just …
Robin Chapman's user avatar