In Evans' PDE text, when proving the solution to Poisson's equation, when he integrates by parts he takes the inward pointing normal, whereas in the integration by parts formula in the appendix, it uses the outward pointing normal.
This is probably a very elementary question but what is going on here?
The fact that it is the inward pointing normal is important and comes in to play in the next few lines. So I'm hoping to get over this minor obstacle!