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The study of differentiable manifolds and differentiable maps. One fundamental problem is that of classifying manifolds up to diffeomorphism. Differential topology is what Poincaré understood as topology or “analysis situs”.

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Accepted

$\varepsilon$-covering number after diffeomorphism

(Since the OP appears satisfied with my comment, I am reproducing it here as an answer.) Fix $\epsilon > 0$. Since $\phi$ is $\mathscr{C}^1$, it must also be Lipschitz-continuous on compact subsets o …
Vidit Nanda's user avatar
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1 vote

Analogue of singularity theory in other categories

A brief account of PL Morse theory has been requested by Andras in the comments, so I am writing it down here. Note that this does not address the main question on PL singularity theory. Note also tha …
Vidit Nanda's user avatar
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4 votes
1 answer
358 views

Classifying smooth embeddings which yield Morse functions

Let $\mu:M \to \mathbb{R}$ be a fixed surjective smooth function on a smooth manifold $M$. Let $N$ be a smooth compact manifold that embeds smoothly into $M$ via $\iota:N \to M$. What conditions o …
Vidit Nanda's user avatar
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1 vote

Lipschitz Approximation to a PW Smooth Map

Here is Ryan Budney's answer from the comments, I'm copying it here so that this question does not re-appear on the front page as unanswered. Let $f:\mathbb{R}\to\mathbb{R}$ be the absolute value f …
3 votes
1 answer
320 views

Measuring almost-critical values of smooth functions.

Consider a compact sub-manifold $X \subset \mathbb{R}^n$ of Euclidean space and let $f:X \to \mathbb{R}$ be any smooth function. Recall that $x \in X$ is a critical point of $f$ if the gradient $\nabl …
Vidit Nanda's user avatar
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7 votes

Good books on Geometric Theory of Dynamical Systems

Pick up (almost) anything by Ethan Akin. I particularly recommend "The General Topology of Dynamical Systems" available on Amazon. Although it is somewhat older than what you indicate you are looking …
12 votes

Can we define Whitney stratification algebraically?

There is a purely algebraic characterisation of Condition (B) due to Le and Teissier, see Proposition 1.3.8 of the paper Lê Dũng Tráng; Teissier, Bernard, Limites d’espaces tangents en géométrie analy …
Vidit Nanda's user avatar
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