Conjectural generalisation of the sewing lemma for approximate actions

Let PP be a metric space, and let ((Mx),(μxy))\big((M_x),\,(\mu_{xy})\big) be an approximate action of the pair groupoid P×PP\times P, with each MxM_x a complete metric space and μxy\mu_{xy} satisfying the estimates of Definition. Let GP\smopLipth\mathcal G_P^{\smop{Lip-th}} denote the Lipschitz thin equivalence groupoid. Conjectural sewing lemma. There exists a unique action φ\varphi of GP\smopLipth\mathcal G_P^{\smop{Lip-th}} such that, for every representative path γ:[0,1]P\gamma:[0,1]\to P of a class gGP\smopLipth\mathbf g\in\mathcal G_P^{\smop{Lip-th}},

dγ(s)γ(t)(φ[γst],μγ(s)γ(t))Cts1+ε.d_{\gamma(s)\gamma(t)}\big(\varphi_{[\gamma_{st}]},\,\mu_{\gamma(s)\gamma(t)}\big)\le C'|t-s|^{1+\varepsilon}.

Here γst\gamma_{st} is the class of the restriction of γ\gamma to [s,t][s,t]. For every choice of γg\gamma\in\mathbf g, φg\varphi_{\mathbf g} is the limit in Cγ(1)γ(0)C_{\gamma(1)\gamma(0)} of the compositions

μγ(0)γ(t1)μγ(t1)γ(t2)μγ(tk1)γ(1)\mu_{\gamma(0)\gamma(t_1)}\circ\mu_{\gamma(t_1)\gamma(t_2)}\circ\cdots\circ\mu_{\gamma(t_{k-1})\gamma(1)}

when the mesh of the subdivision (0,t1,,tk1,1)(0,t_1,\ldots,t_{k-1},1) tends to zero. One possible constant is

C=21+εg(Lip(γ)ts)(i=1nCi)ζ(1+ε),C'=2^{1+\varepsilon}g\big(\operatorname{Lip}(\gamma)|t-s|\big)\left(\sum_{i=1}^nC_i\right)\zeta(1+\varepsilon),

and the action satisfies

Lip(φg)g(infγgLip(γ)).\operatorname{Lip}(\varphi_{\mathbf g})\le g\Big(\inf_{\gamma\in\mathbf g}\operatorname{Lip}(\gamma)\Big).

This is presented as a conjectural generalisation of the paper's main sewing theorem from local approximate flows to approximate actions over a metric parameter space. The statement asserts existence, uniqueness, convergence of subdivision compositions, a quantitative error estimate, and a Lipschitz bound, but the supplied text gives no resolution status.

Sources & referencesView supporting material

Primary source

Charles H. A. Curry and Dominique Manchon, “Sewing lemma and knitting lemma for metric spaces”, arXiv:2512.05312 (2025).

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