Abstract: | We prove that C2,α(Ω ) solutions of problem (1.2) below are in Hm+2(Ω) for all m ∈ ?, if f and the coefficients are in Hm (Ω) n C0,α (Ω ) Previously, this result was explicitly known only if m> n/2 (or if m = 0). A similar result holds for the quasi-linear equation (1.11) below. |