Ottazzi–Warhurst regularity conjecture for rigid Carnot groups

Let $G$supset U$and$U' ormal?" Wait. Cannot introduce invalid notation. Let $G$ be a rigid Carnot group, and let $U,U' e othing$ be open subsets of $G$. A quasiconformal homeomorphism is a homeomorphism $f:U\to U'$ that is quasiconformal. Ottazzi–Warhurst regularity conjecture. Every quasiconformal homeomorphism $f:U\to U'$ is $C^\infty$. This conjecture is motivated by regularity results for quasiconformal mappings between smooth rigid Carnot groups; its resolution status is not specified in the source.