Show HN: PDF/ePub reader where you ask AI and each answer links to the passage

A developer released a browser-based PDF and EPUB reader, announced on Hacker News as a Show HN post, that lets readers ask an AI questions about a document and returns answers with citations linking to the exact passage. The reader keeps the file and its search index in the browser and never uploads the document, and it offers a reflowing text view, four highlight colors, notes, and highlight-linked conversations. The tool is available with no installation, and an account syncs progress, highlights, notes and conversations across devices.

Open the file Open a PDF or an EPUB from your device. It is saved in your browser and never uploaded anywhere. Nothing to install. AI reader for PDF and EPUB Open a PDF or an EPUB in your browser, read it without zooming, even on your phone, and ask what you do not understand. Every answer cites the exact passage and one tap takes you there. The file never uploads anywhere. The prediction is that if an object is sufficiently dense, it will collapse in upon itself and be surrounded by an event horizon from which nothing can escape. Karl Schwarzschild was the first person to note this phenomenon in 1916, but at that time, it was considered mostly to be a mathematical curiosity. The Schwarzschild radius is also called the event horizon of a black hole. We noted that both space and time are stretched near massive objects, such as black holes. However, if a neutron star gains additional mass, it would eventually collapse, shrinking beyond the Schwarzschild radius. Once that happens, the entire mass would be pulled, inevitably, to a singularity. In the diagram, space is stretched to infinity. Time is also stretched to infinity. As objects fall toward the event horizon, we see them approaching ever more slowly, but never reaching the event horizon. As outside observers, we never see objects pass through the event horizon: effectively, time is stretched to a stop. It is not a chat next to a PDF. It is a reader with the AI in the margin: you read, you ask, you check , all without leaving the page. About any part of the book or the paragraph you select, in your language. The AI answers with the book's passages in front of it and tells you when something is not in it. Every answer carries its citations. Tap a number and the book jumps to the passage, highlighted. If the AI gets it wrong, you see it right there. No zooming, no dragging from side to side, no words cut in half. Text view reflows the PDF so the text fits your screen and the font size you choose. The original page is one tap away. Try it: tap “Text view” and watch how the very same page adapts to your screen. Chapter 4 · Processes The scheduler decides which process gets the CPU at every instant. The simplest policy serves in order of arrival, and its flaw is well known: a long process holds the CPU while short ones wait behind it, and the average response time explodes. The classic alternative splits time into quanta. Each process gets a slice and goes back to the queue. The cost is the context switch, which is not free: save registers, invalidate the cache, restore the memory map. Measuring that cost precisely requires hardware counters, because the system clock is far too coarse for slices of a few microseconds. A real sched- uler combines both ideas with priority queues that age, so no process is left without a turn indefinitely. The core loop fits in a few lines: while queue empty &rq { task t t = dequeue &rq ; run for t, QUANTUM US ; if t- state == RUNNABLE enqueue &rq, age t ; } With aging, a process's effective priority grows with the time it has been waiting, which bounds the maximum latency to a multiple of the quantum. 118 Remember that each file in your working directory can be in one of two states: tracked or untracked. Tracked files are files that were in the last snapshot; they can be unmodified, modified, or staged. Untracked files are everything else. When you first clone a repository, all of your files will be tracked and unmodified because Git just checked them out and you haven't edited anything. Highlight in four colors, write a note next to it and ask from the highlight : the conversation stays linked to the passage. With an account, progress, highlights, notes and conversations wait for you on your phone. Change the font size or the theme and every highlight stays on its sentence. The file and the index for searching inside it stay in your browser. When you ask, only your question and the passages needed to answer it travel, and the answer comes back with its citations. With an account, the book's text also passes through the server to build the search index, and it is not stored. The trade-off: with an account, on another device you will see the book in your library with your notes inside, but you need to open the file there once to keep reading. A two-column paper, a statute, a programming manual or a textbook. Pick your field and try it with a real document like the ones you will open. A textbook or a two-column paper, readable on your phone. Ask about a clinical picture and the answer takes you to the passage that explains it. Tested with PAPPS 2020 and The LancetSee it with a real paper Open the statute or the syllabus and ask about an article: the answer cites the text and takes you to it so you can check. Tested with the GDPR and the BOESee it with a real statute Specifications, RFCs and technical books with syntax colors. Select a block of code and ask what it does. Tested with Pro Git and RFC 9110See it with Pro Git Formulas are preserved in text view and, with an account, you can tap one to ask about it. Tested with OpenStax and GutenbergSee it with a textbook Start now, no sign-up. If Marginalia becomes part of your routine, install it as an app and your books wait for you in the library.