\begin{waffle} I have recently borrowed Serge Lang's "Challenges" from the library. I had heard about it for several years but had not had the opportunity to see it. (I could only locate five copies in French university libraries and had to use interlibrary loan.) I first thought I would read only one or two chapters but ended up reading the whole book in a few days. \end{waffle}

##Motivation##

I do not want to get subjective or argumentative here, suffice it to say that I hold Lang's attitude and views in very high esteem, and this provides motivation for this question.

##Background##

For some background on Lang and his files, one can read the first part of Lang's obituary in the AMS Notices at http://www.ams.org/notices/200605/fea-lang.pdf.

The book "Challenges" was published in 1997. I guess Lang went on to gather documentation regarding several cases dealt with in the book after its publication. Consequently, several related files must have contained much more documentation at the time of Lang's demise than at the time of "Challenges" publication. Besides, "Challenges" does not deal with all the cases Lang has been involved with and interested in.

In addition, the AMS obituary mentions that Lang "has some unpublished books of a political nature".

Are the full (i.e. the whole documentation that Lang had gathered and arranged) files regarding the "Challenges" cases (i.e. those dealt in that book) published somewhere? If not, are they available in some other form? What has happened to Lang's related personal papers?

What about other files not reproduced in "Challenges"? What are they, and where is the documentation?

Same question for Lang's "unpublished books of a political nature".