12 TUGboat, Volume 37 (2016), No. 1

푛 The libertine gets mathematical 푛 푛 푘 푛−푘 (푥 + 훼) = ∑ ( )푥 훼 Khaled Hosny 푘=0 푘 −푥, 푥 < 0 Linux Libertine is a popular libre font family (re- |푥| = { 푥, 푥 ≥ 0 leased under the SIL Open Font License) and one of 휕2휓 휕2휓 휕2휓 the early to be designed from the ground ∇ ⋅ ∇휓 = + + up as a libre project. Together with its organic sans- 휕푥2 휕푦2 휕푧2 companion, Linux Biolinum, they serve as an 1 휕 휕휓 excellent type family for many scholarly works. = sin 휃 푟2 Due to their attractiveness, Linux Libertine and 푟2 sin 휃 [ 휕푟 ( 휕푟 ) Linux Biolinum fonts are often used for mathemati- Figure 1: Sample휕 of Libertinus휕휓 Math1 휕2휓 cal and other scientific works heavy in mathematical + sin 휃 + ( ) 2 typesetting, but the lack of a mathematical compan- 휕휃 휕휃 Libertinussin 휃 휕휑 Serif] ion forced people to try to find matching mathemat- Libertinus Serif Italic ical typefaces with varying degrees of success. A Libertinus Serif Semibold mathematical companion was thus one of the most Libertinus Serif Semibold Italic requested features for this type family. Libertinus Serif Bold In late 2012 I started playing with the idea of Libertinus Serif Bold Italic creating a mathematical companion for this family Libertinus Serif Display using the existing text characters for basic mathemat- Libertinus Sans ical alphabets, adding an OpenType MATH table, Libertinus Sans Italic and some symbols needed for basic mathematical Libertinus Sans Bold typesetting. I got the basics working, but then had Libertinus Math to put it on the back burner for a while. In 2014 TUG Libertinus Mono showed interest in funding the development of this Libertinus Keyboard mathematical companion and work resumed. Devel- Figure 2: List of Libertinus fonts opment took a while, as usual, but in January 2016 the was finally released. Linux Libertine and Linux Biolinum are big like X TE EX, LuaTEX, Mozilla Firefox, and MS Office, typefaces with thousands of that were de- among others. Unfortunately, it cannot be readily veloped over the course of almost 10 years, and it used with traditional TEX implementations that lack had accumulated many issues over the time. While support for such fonts. working on the mathematical companion, I couldn’t The work on the mathematical companion in- help but try to fix many of these issues, and after volved using the existing serif and sans-serif glyphs a while it became clear that this is becoming a full to provide corresponding mathematical alphabets, fork of the original project, not just an additional drawing a missing lower case for the blackboard member of the family. alphabet, and adding many missing mathematical With this in mind, I went ahead and made it a symbols and big variants to cover symbols used in full fork. Since the original typefaces use the OFL plain TEX and the LATEX kernel. Not all alphabets “reserved names” clause, I had to rename my modified are covered, though. There are no script, fraktur, fonts. I first wanted to just drop the “Linux” part and sans-serif bold italic, or typewriter alphabets. release under the name “Libertine” (why should a The original Linux Libertine fonts were devel- typeface be named after an kernel?), oped using free software, mainly FontForge. That but it turns out I can’t use either of the words “Linux” tradition continues in this fork, but replacing Font- or “Libertine” in my fork, not just the combined Forge by its fork Sorts Mill Editor (bitbucket.org/ name. Fr´ed´ericWang suggested the Latin word sortsmill/sortsmill-tools), and adding (a fork “Libertinus” which I liked much, so Linux Libertine of) FontTools (.com/behdad/fonttools) to became Libertinus Serif and Linux Biolinum became the mix. Libertinus Sans, with the brand new mathematical The new font files can be downloaded from: companion being named Libertinus Math. github.com/khaledhosny/libertinus/releases Libertinus Math is an OpenType font with a ctan.org/pkg/libertinus MATH table, so it can be used only with a mathe- matical typesetting engine that supports such fonts,  Khaled Hosny khaledhosny.org

Khaled Hosny