Gałęski's local smooth rank-constrained approximation conjecture

From papers

Let 1m<n1\leq m<n be integers and let ΩRn\Omega\subset\mathbb R^n be open. If fC1(Ω,Rn)f\in C^1(\Omega,\mathbb R^n) satisfies rankDfm\operatorname{rank} Df\leq m everywhere in Ω\Omega, then for every point xΩx\in\Omega there is a neighborhood Bn(x,ε)Ω\mathbb B^n(x,\varepsilon)\subset\Omega and a sequence fiC(Bn(x,ε),Rn)f_i\in C^\infty(\mathbb B^n(x,\varepsilon),\mathbb R^n) such that rankDfim\operatorname{rank} Df_i\leq m and fif_i converges to ff uniformly on Bn(x,ε)\mathbb B^n(x,\varepsilon).

Gałęski's local approximation conjecture. Every such mapping admits, around each point, a uniformly convergent smooth approximation sequence preserving the derivative-rank bound.

The paper states that this weaker local form is also false in general, with the main result providing counterexamples for certain ranges of nn and mm.

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Sources & referencesView supporting material

Primary source

Paweł Goldstein and Piotr Hajłasz, “C^1 mappings in R^5 with derivative of rank at most 3 cannot be uniformly approximated by C^2 mappings with derivative of rank at most 3”, arXiv:1804.08289 (2018).

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