ABSTRACT
In this chapter, we begin the analysis of elliptic equations, considering the equation λ u − A u = f https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780429262593/03624a6d-a4e5-45fb-ba52-c2b8f08b80c3/content/math10_1.tif"/>
