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Sender: Mailing list for the LaTeX3 project <[log in to unmask]>
Date: Wed, 25 Aug 2021 17:45:13 +0100
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From: Jonathan Fine <[log in to unmask]>
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Summary: I think Portable TeX Documents are a great idea. (Disclaimer: I'm
the inventor.) Come to tomorrow's TeX Hour to discuss.

Date and time: Thursday 26 August, 6.30 to 7.30pm UK time.
UK time now:
Zoom URL:

Adobe released PostScript (PS) in 1982, and Portable Document Format (PDF)
in 1993. Many production and user problems in PS were fixed in PDF, which
remained a proprietary standard until 2008. PS and PDF were both based on
very sound technical and business decisions. PDF so to speak created a safe
and self-contained world for the distribution of typeset documents. PS and
PDF are both page description languages.

In 1982 Don Knuth created a safe and self-contained world for typesetting
that was rapidly adopted by mathematicians and physicists. It includes the
DVI page description language.  PDF arrived 11 years after TeX,  and Sergey
Lesenko's DVIPDF followed three years later.

TeX produces identical outputs, given identical inputs. PDF does something
similar. It also has a structured storage system for storing fonts,
graphics, multimedia objects and other resources. This allows PDF to
guarantee identical inputs to its page description language.

I firmly believe that Portable TeX Documents (PTD) will greatly benefit TeX
users and developers, just as PDF benefitted its users, developers and
Adobe. As a loyal and responsible member of the TeX community, I feel
obliged to share this opinion with the community, both promoting it and
fairly considering objections and alternatives.

You're invited to tomorrow's TeX Hour: Portable TeX Documents (PTD).
Date and time: Thursday 26 August, 6.30 to 7.30pm UK time.
UK time now:
Zoom URL:
Meeting ID: 785 5125 5396
Passcode: knuth

Here's a technical teaser. Each PTD has document and typesetting inputs,
and optionally typesetting outputs. Every tree of files checked into git
has a secure hash, which is unfeasible to forge. These secure hashes are
keys that characterize the PTD, including its inputs and outputs.

Besides version control, git is very efficient at turning a secure hash
into its tree of files, provided it has access to a repository that
contains all files in the tree. All font metric and style files that have
ever been uploaded to CTAN will occupy only a few gigabytes when stored in
git, and most TeX documents will require perhaps only 50MB of such files.

So downloading on the fly resources required from the typesetting of a TeX
source document is entirely practical. The source could be CTAN, or
somewhere else. This is because git is a peer-to-peer distributed file
system. Further, like a well set up website, git doesn't fetch resources
it's already got.

One hard part of implementing PTD, besides getting resources and overcoming
inertia, is specifying the exact form of the resource tree of a PTD. I hope
that once that part is in practice solved others will use it. This will
allow other parts of the standard to evolve. It took Abode 11 years to go
from PostScript to PDF.


Last week's TeX Hour was on XML to (La)TeX to PDF.  Digital Humanities met
Mathematics and Physics. The videos are available at

Happy TeXing