“…Under these assumptions one has that solutions in the range p ≥ 2 have Hölder regular horizontal gradient. This is a formidable achievement in itself, building on contributions by several authors [Cap97,Dom04,DFDFM05,MM07,DM09a,MZGZ09,DM09b,Ric15], with the final result being established eventually by Zhong in [Zho10]. Beyond the Heisenberg group one has some promising results due to Domokos and Manfredi [Dom08,DM10b,DM10a] in the range of p near 2.…”