Hölder regularity for weak solutions of diagonal divergence quasilinear degenerate elliptic systems

In this paper, we establish Hölder regularity for weak solutions of a class of diagonal divergence quasilinear degenerate elliptic systems of Hörmander's vector fields when the coefficients belong to the class of VMOX functions with respect to x and uniformly with respect to u, and the lower order terms satisfy a natural growth condition.