Extremals for a series of sub-Finsler problems with 2-dimensional control via convex trigonometry A.A. Ardentov, L.V. Lokutsievskiy and Yu.L. Sachkov ESAIM: COCV, 27 (2021) 32 Published online: 30 April 2021 DOI: 10.1051/cocv/2021024