I would like to know if there is a book (or a paper) which can give me an introduction to LAP. I tried to read some papers by myself, but I don't feel comfortable. I think that I need the basic ideas behind this tool.
I apologize for being too vague.
Thank you for any suggestions.



Limiting absorption principle
Well, there's Terence Tao's [blog](https://terrytao.wordpress.com/2011/04/21/the-limiting-absorption-principle/) on this topic, you can't go wrong starting from there.


For a more extensive intro, with many references, you could take a look at this Ph.D. thesis:
[The Principles of Limit Absorption and Limit Amplitude for Periodic Operators](http://digbib.ubka.uni-karlsruhe.de/volltexte/documents/1638853)


