“…Furthermore, in [23,9,10], more than the Hölder continuity, an optimal L p theory for weak solutions to (inhomogenous version of) (1.5), (1.7) and (1.10) was established. There are also alternative ways to derive Hölder continuity (or L p theory) of (1.5), (1.7) and (1.10); we refer the readers to [22,25,8,6] for more information.…”