Is there a basic book (accessible to beginning graduate students in real analysis -- not quite PDE theory) on high-order PDE? In particular, I'd like to know what type of boundary conditions (and why) people like to use for high-order elliptic problems. And perhaps a little about the associated Green's functions. I've managed to dig up Polyharmonic Boundary Value Problems, but it's a little too advanced for me, jumping right into heavy analysis -- I'm seeking a more basic book/lecture notes if they exist!
Many thanks