1. Alfonseca, A., Auscher, P., Axelsson, A., Hofmann, S., Kim, S.: Analyticity of layer potentials and L 2 Solvability of boundary value problems for divergence form elliptic equations with complex $$L^{\infty}$$ coefficients, preprint
2. Auscher P. (1996). Regularity theorems and heat kernel for elliptic operators. J. London Math. Soc. 54(2): 284–296
3. Auscher, P., Tchamitchian, Ph.: Square root problem for divergence operators and related topics. Astérisque No. 249 (1998)
4. Campanato S. (1965). Equazioni ellittiche del IIº ordine espazi $${\mathcal{L}}^{(2,\lambda)}$$ . (Italian) Ann. Mat. Pura Appl. 69(4): 321–381
5. De Giorgi E. (1957). Sulla differenziabilità e l’analiticità delle estremali degli integrali multipli regolari. (Italian) Mem. Accad. Sci. Torino. Cl. Sci. Fis. Mat. Nat. 3(3): 25–43