## PrefacePreface to 2016 Edition

In April 2016, the American Institute of Mathematics hosted a weeklong workshop in San Jose to introduce authors of open textbooks to git and Robert A. Beezer's MathBook XML authoring language designed to seamlessly produce HTML, , and other formats from a common XML source file. I (MTK) attended and eagerly began the conversion of existing source for this now decade-old project into MathBook XML. David Farmer deserves an enormous amount of credit for automating much of the process through a finely-tuned script, but the code produced still required a good deal of cleanup. This edition, the first not labeled “preliminary”, will hopefully become the first of many annual editions of Applied Combinatorics released under an open source license.

The main effort in producing this 2016 edition was to successfully convert to MathBook XML. Along the way, I attempted to correct all typographical errors we had noted in the past. There are undoubtedly more errors (typographical or otherwise) that will be corrected in future years, so please contact us via email if you spot any. The text now has an index, which may prove more helpful than searching PDF files when looking for the most essential locations of some common terms. Since MathBook XML makes it easy, we now also have a list of notation. Instructors will likely be glad to know that there were no changes to the exercises, so lists of assigned exercises from past years remain completely valid. 1  The only significant changes to the body of the text was to convert WTT's code snippets from C to Python/SageMath. This has allowed us to embed interactive SageMath cells that readers who use the HTML version of the text can run and edit. We've only scratched the surface with this powerful feature of MathBook XML, so look for more SageMath additions in future years.

There are two exceptions to this. The first is that Exercise 8.8.7 has been modified to make the computations involved cleaner. We have preserved the exercise that was previously in this position as Exercise 8.8.27 and added a hint. The second is that a coefficient was changed in Exercise 9.9.15 to make the exercise feasible.

The conversion to MathBook XML allows us to make a wider variety of formats available:

• HTML: With responsive design using CSS, we feel that the text now looks beautiful on personal computers, tablets, and even mobile phones. No longer will students be frantically resizing a PDF on their phone in order to try to read a passage from the text. The “knowls” offered in HTML also allow references to images, tables, and even theorems from other pages (or even a distance away on the same page) to provide a copy of the image/table/theorem right there, and another click/tap makes it disappear.

• PDF: Not much is changed here from previous years, other than the PDF is produced from the that MathBook XML generates, and so numbering and order is consistent with the HTML version.

• Print: Campus bookstores have frequently produced printed versions of the text from the PDF provided online, but we have not previously been able to provide a printed, bound version for purchase. With the 2016 edition, we are pleased to launch a print version available through a number of online purchase channels. Campus bookstores may also acquire the book through wholesale channels for sale directly to students. Because of the CreativeCommons license under which the text is released, campuses retain the option of selling their own printed version of the text for students, although this is likely only financially advantageous to students if only a few chapters of the text are being used.

We have some ideas for what might be updated for the 2017 Edition (e.g., Chapter 4 needs to be expanded both in the body and the exercises, Chapter 8 would benefit from integration of SageMath to assist with generating function computations, and Chapter 16 is still not really finished). However, we would love to hear from those of you who are using the text, too. Are there additional topics you'd like to see added? Chapters in need of more exercises? Topics whose exposition could be improved? Please reach out to us via email, and we'll consider your suggestions.

Mitchel T. Keller
Lexington, Virginia