Higher differentiability for n-harmonic systems with Sobolev coefficients

We provide a higher differentiability result for the finite energy solutions u∈W1,1(Ω,RN) of a degenerate elliptic system of the formdivA(x,Du)=0inΩ⊂Rn, where Ω is a bounded open set in Rn and A(x,ξ) is a degenerate elliptic operator. The function which measures the degree of degeneracy of the problem is assumed to belong to the Sobolev class W1,n(Ω).