Same here - I was excited to see this kind of book, as I'm trying to improve my maths knowledge and the conciseness and structure of Ivan's book was attractive, but no eBook option stopped me right there.

While we're on the topic of exams, I've recently came across the following book[1] that deals specifically with doing better in maths heavy exams - you might want to have a look whether it's something that can help you in your exams:

[1] Exam Mastery - How to excel in maths-heavy exams http://www.amazon.com/Exam-Mastery-excel-maths-heavy-ebook/d...

An ebook being cheaper isn't a big deal for me, since my view is the price more to do with the content than the format. For other people it does seem to be more significant though. Maybe it should be the price of the physical book less the costs of printing/binding/etc. such that you get the same amount of money in the pocket at the end? (I don't know if that's how it works, having never published a book!)

PDF is good for PC viewing and will work on pretty much everything, though EPUB and Kindle formats will make things better on e-readers and phones/tablets since they support re-flowable content, but I guess would probably require more work on your part to support.

> Is a DRM-free PDF good enough or should I do the .epub format?

Definitely epub, makes it just much easier to read, at least on my used platforms (kindle, ipad mini)

Why not offer all three?

Excellent - I'd be willing to spend around $20 - PDF is my preferred format (iPad and Desktop PC), but agree with notdrunkatall, why not offer all three.

Thank you. PDF all the way for all books. GoodReader on Retina iPad.

Please please please do an ePub version. PDF is great for reading on a computer, but an ePub is miles better on an iPad. I'll buy a digital copy if it comes in ePub, but not if it's only PDF.