For the impatient: TeX Writer Latest Version on iOS App Store TeX Writer (previously TeX Notebook) v1.1 is a major update:

• Fast compilation right on your iPad, no internet connection required;
• Add LaTeX base;
• Add AMSTeX, AMSLaTeX, AMS Fonts;
• Log viewer now links to error lines.  With this release, TeX Writer can do much more than just taking notes, hence the name change. Serious scientific writing can be done on iPad now. The DVI viewer crops the page according to different paper sizes in the \documentclass setting, so that you can have a readable fullscreen preview on iPad screen.  

  This app comes with AMS TeX, AMS LaTeX, AMS Fonts preinstalled. If you need additional packages, just dump them all in the Documents folder. We'll come up with a more reasonable solution in future. Although we did a lot of tests, unfortunately, a bug has slipped through. Sometimes when you are rotating screen, the accessory keyboard doesn't get updated after the orientation is changed, so that keys on the right edge may not be accessible. We'll fix it in next update. For the time being, a work around is  to do some more rotation until it is updated correctly. The readme.tex still says it's plain TeX only. It's not true. We'll correct it next time:-) Now, the beauty of LaTeX on iPad must be seen to be belived:

Download TeX Writer now!

Special thanks goes to D.E.K for the long lasting gem, and the LaTeX community for the wonderful extensions. Special thanks also goes to Andrew Stacey for the warm encouragements, countless suggestions and beta testing. Asking for a favor If you like TeX Writer, please post your review in App Store! We'll really appreciate your kindness.

You may ask (because someone else already did): 1. Isn't this long regarded impossible? It is true that I have been trying this problem for really a long time, but I don't want to pretend it is a big achievement. Actually what you have to do is to cut kpathsea loose and make TeX reentry-able.   The whole process is no doubt a nightmare, however, with a little patience you can get through. 2. You must have violated GPL! Well, No GPLed components are used in this app. TeX and web2c are in public domain, LaTeX has its own open license, and I wrote the DVI render myself. Did I miss something?