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For questions requesting examples of a certain structure or phenomenon

9 votes

What's the use of Malgrange preparation theorem?

Take $k=1$ in your statement. There are two easy cases: the first one is when $f$ is real-valued, then you have only to use the implicit function theorem to get a normal form $t+a(x)$, up to a unit (a …
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5 votes

Example for the Sobolev embedding theorem when p=n.

Take $u$ in $\mathscr S'(\mathbb R^2)$ with $$ \hat u(\xi)=\frac{\mathbf 1(\vert\xi\vert\ge 2)}{\vert\xi\vert^3 \ln\vert\xi\vert},\quad \vert \xi\vert^2\hat u(\xi)=\frac{\mathbf 1(\vert\xi\vert\ge 2)} …
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1 vote

Is there a non-trivial example for a 1-homogeneous function satisfying a specific inequality...

Take $A(x)=\vert x\vert$ the Euclidean norm in $\mathbb R^n$, which is obviously homogeneous of degree 1. We have $$ A'(x)=\frac{x}{A(x)},\quad A''(x)=\frac{Id}{A(x)}-\frac{x\otimes x}{A(x)^3}=A(x)^{- …
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