{An interactive \iOS\ math book using a new \TeX\ interpreter library} {Doug McKenna} {The current \TeX\ ecosystem is geared towards creating only static \PDF\ or other output files. Using a re-implementation of a \TeX\ language interpreter as a library linked into an \iOS\ client program that simulates a document on a device with a touch screen, the author will demonstrate a new \PDF-free ebook, \emph{Hilbert Curves}, that typesets itself each time the application launches. The library maintains all \TeX\ data structures for all pages in memory after the typesetting job is done, exporting pages as needed while the user reads the book and interacts with its dynamic illustrations. This design also allows text-searching the document's \TeX\ data structures while the ebook is ``running''.}