Open source LaTeX lecture notes/slides/books In the mathematics community it's quite common for professors to write their own notes for the classes they are teaching. The notes are then usually published in both PDF and PS form on the course website. However, it's extremely rare to see anyone publish the LaTeX source code for their notes and slides. As a student this has always bugged me while as an instructor this has to me seemed like something obvious to do, meaning I don't see how it could hurt and it can only help, so why not do it?
Here are a few reasons for publishing source code for notes:


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*Makes it possible for students to easily create condensed versions of the notes for future review.

*They can easily edit the text and add their own comments to it if something is unclear or they can even replace a proof with one of their own, if another proof seems more natural to them. They can also edit them to remove material that's obvious/known to them, thus making the notes quicker for them to read.

*If a student in the class has a habit of typing up their own notes, they will be able to copy paste e.g. statements of definitions and theorems from the class notes, which will save them considerable time.

*There are flashcard programs out there like e.g. Mnemosyne and Anki that support LaTeX input. Having the source code would make it considerably faster to create cards for e.g. precise definitions and statements of theorems. Especially in fields like algebra, algebraic geometry etc. which have tons of terminology, this could be useful for quick memorization while learning material for the first time.
My questions is then: why aren't most people publishing source code? Is this something they just haven't thought about? On the other hand, as a student I asked professors for the source code quite a few times and my request often got rejected with no explanation.
As an aside I might add that I grew up as a teenager in the early 90s hacking on Linux, so open source has always seemed like the "right" idea to me for any knowledge sharing.
 A: Here my reason for not doing it (I usually teach rather elementary courses).
It will result in a large set of edited notes I have no control on. This means that some of those edited notes may well contain errors or do not reflect the spirit of my course and at the same time be very popular between students for being "condensed", "easy to read", "good to pass the exam". This will damage some students, that can get something wrong from the course because of sloppiness. 
Also, as a personal experience, at least on one occasion I had someone trying to get some money out of my notes. Starting from the source file it would be even easier for them to rearrange the file in a form that makes it even harder to give them some trouble for this behaviour.
On the other hand we now have rather professional Pdf-Notes like softwares that allow everyone to underline, put on evidence, highlight whatever they want. With the positive point, though, that such modifications of the original file are clearly identified for what they are: additional material.
A: I have lots of undergraduate notes in PDF form on my web pages (http://shef.ac.uk/nps).  No one has ever asked me for the source files.  Nonetheless, I have thought about releasing them explicitly in LaTeX form under a creative commons license.  This has not happened for fairly mundane reasons:


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*Some of the notes are partially based on earlier notes by colleagues, and I have not discussed things with them.

*Most courses have a fairly elaborate setup with separate files for notes, problem sheets and lecture slides, auxiliary files that are \included in the main files, Maple worksheets used to generate jpeg diagrams and so on.  I have not worked out a good way to package everything.

*All my courses have detailed solutions to all the problems, which I release to students a week or so after the problems have been assigned.  I have not decided what would be the best thing to do with such solutions if I were to make the source files freely available.  At the moment I have things set up so that the solutions are in the same files as the problems, with LaTeX macros etc to switch them on and off.
A: I see no problem with publishing LaTeX source codes for books and more-or-less stable versions of lecture notes. However, I often feel that what I have written is not mature enough, and it seems that there is not much point in publishing the source code if you are not completely satisfied with the current version.
I agree with you generally though. In fact I started releasing source codes for homework problem statements since some students like to type their homework solutions in LaTeX and having the statements' source code would save them some time. 
