[R] Offtopic --- book references

[kjetil brinchmann halvorsen]

Hola!

I am about to do this years buying for our library, and could need
help with some references. 

Some people here will start to work with IRT and Rasch models. 
>From the book descriptions on Amazon it is difficult to decide
what books to buy. 

I want one introductory book on IRT/Rasch, and one more
profound, with sufficient detail to actually start coding. 

Anybody knows some good books satisfying this criteria?

Kjetil Halvorsen