I am reading some papers on Green functions of elliptic equations. Here the elliptic systems is stated as $ Lu=-\operatorname{div}(A\nabla u) $ where $ A(y)=(a_{ij}^{\alpha\beta}(y)) $ is a matrix valued function in $ \mathbb{R}^{d} $ and $ 1\leq i,j\leq d $, $ 1\leq\alpha,\beta\leq m $.
I have read the paper named "The Green function estimates for Strongly elliptic systems of Second Order" and the paper delt with the situation that the dimension $ d\geq 3 $. I want to know about the the case when $ d=2 $. Can you give me some references?