linjaaho writes: "I have found that there are many high-quality science textbooks that are out-of-copyright because 70 years has passed from the death of the original author. For 99 % in cases, 70+ years is too old to be used in teaching. But there are also many Finnish and English textbooks that are 10-20 years old but out-of-print, and could be published free online by just asking the permission from the original author. But I have a technical problem: how to digitize a book containing lots of math formulae, and where to publish it online? I know Project Gutenberg, but they only support books with text and photos."