@Misc{ MagMin19, author = { Magnani, Valentino and Minne, Andreas }, title = { Optimal Regularity of Solutions to No-Sign Obstacle-Type Problems for the Sub-Laplacian }, journal = { Anal. PDE }, year = { 2021 }, pages = { }, URL = { http://cvgmt.sns.it/paper/4403/ }, note = { cvgmt preprint} }