Stream: Beginner Questions

Topic: Adding more symbols to Isabelle-UTF8

Ant S. (Feb 20 2026 at 13:48):

From this message I realize that there are two buffers in Isabelle: one to handle UTF8 symbols and the other to convert those symbols to ASCII. #Beginner Questions > Setting up Isabelle/VSCode @ 💬

Is it possible to add more UTF8 symbols? It seems like it is possible by modifying /etc/symbols. However, I wanted to know if user-defined symbols can be imported when opening an existing project. For example, when I pull a repo and open it in Isabelle/jEdit or Isabelle/VSCode, it auto-imports custom symbols.

Fabian Huch (Feb 20 2026 at 14:16):

Don't let yourself be confused by that discussion about technical internals.

Isabelle symbols are independent on the concrete encoding. They can be defined in the user home (but not for a project IIRC) and arbitrarily extended. For rendering, those symbols may be assigned a unicode glyph in a certain encoding (e.g., UTF-8).

However, you will find that a unicode glyph alone is not very helpful: You also need a font that can render it. For that, you need to add glyphs in the font base, build the fonts, and re-assemble Isabelle components.

Ant S. (Feb 20 2026 at 14:17):

My default font renders the extensions I'd like to make just fine; the symbols in question are ⸢ these two ⸣

Ant S. (Feb 20 2026 at 14:23):

Fabian Huch said:

They can be defined in the user home

the user home being the location where Isabelle is installed?

Ant S. (Feb 20 2026 at 14:24):

the symbols file, to my understanding, is like a global environment variable. Can we make a local file that overrides this symbols file if need be? I guess this is slightly different from saying that it is defined for a given project, because that would imply having some sort of project file, and I'm not sure if that's the case in Isabelle

Fabian Huch (Feb 20 2026 at 14:41):

In ISABELLE_HOME_USER/etc/symbols - I don't know what you mean with environment variable here.
See the system manual for an overview about session / component specification, settings, etc. (though symbols are explained in the jedit doc).

Ant S. (Feb 20 2026 at 15:13):

thanks!

Last updated: Mar 04 2026 at 20:34 UTC