I'm trying to learn the Pansu differentiability theorem and I need to know what Carnot groups are. Can someone please explain what Carnot groups are? An introductory reference would be greatly appreciated as well.
Thanks.
I'm trying to learn the Pansu differentiability theorem and I need to know what Carnot groups are. Can someone please explain what Carnot groups are? An introductory reference would be greatly appreciated as well.
Thanks.
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A Carnot group is a special type of Lie group $\mathcal{G} $ that is nilpotent (almost abelian) and simply connected. Its Lie algebra $\mathcal{g}$ gives a nilpotent stratification consisting of $k$ steps. This can be represented in the form $\mathcal{V}_1\oplus\cdots \oplus \mathcal{V}_k$ with $[\mathcal{V}_1,\mathcal{V}_m]=\mathcal{V}_{1+m},~m=1,\cdots ,k-1$. For example, the space $\mathbb{R}^n$ under the binary operation of addition is a commutative Carnot group. Carnot groups possess a Carnot-Caratheodory metric (a metric space with integer Hausdorff dimension greater than its dimension) and Pansu derivative (a special type of derivative adapted to a Carnot group).