Use lualatex for correct ligatures

Technical Story: https://github.com/latextemplates/scientific-thesis-template/issues/54

Context and Problem Statement

For high-quality documents, the ligatures have to be right. See english.stackexchange.com for a long discusisson. See a German rant on wrong ligatures: https://web.archive.org/web/20150425155310/http://www.mengensatz.de/blog/?p=79. For instance, in the English word “offline”, the letters “f” and “l” must not be joined. In the German word “Auflage”, the letters “f” and “l” must not be joined. See also the last lines in https://tex.stackexchange.com/a/64457/9075.

More readings

• https://www.typolexikon.de/ligatur/
• Questions on ligatures: https://tex.stackexchange.com/questions/tagged/ligatures
• Disable ligatures in headings: https://tex.stackexchange.com/q/198743/9075

Considered Options

• Use lualatex+selnolig
• Use a post-processor
• Supress ligatures completely
• Ignore ligature issues

Decision Outcome

Chosen option: “lualatex”, because comes out best (see below).

Pros and Cons of the Options

Use lualatex+selnolig

The only way to keep ligatures where appropriate is to switch to lualatex. There is selnolig. Found going from https://tex.stackexchange.com/q/28437/9075 to https://tex.stackexchange.com/q/63005/9075 and finally to https://tex.meta.stackexchange.com/questions/2884/new-package-selnolig-that-automates-suppression-of-typographic-ligatures

• Good, because disables at the right places and not completely
• Bad, because needs switch of latex compiler to lualatex, which users are not used to

Use a post-processor

• perl-based solution: http://ctan.org/pkg/rmligs
• java-based solution: http://www.ctan.org/pkg/delig (used by @sieversmartin)

• C-based solution (working for German documents only): https://ctan.org/pkg/ligatex

• Good, because proven solutions
• Good, because pdflatex can be used
• Bad, because babel’s "| shortcut is used, which produces currect results in the case of “fl” and the font “latin modern” only. See https://tex.stackexchange.com/a/389439/9075 for a long explanation.
• Bad, because tex files change

Supress ligatures completely

See https://tex.stackexchange.com/q/61042/9075 and https://tex.stackexchange.com/q/1841/9075

• Good, because easy to implement
• Good, because pdflatex can be used
• Bad, because ligatures look better

Ignore ligature issues

• Good, because latex users are used to ligatures everywhere
• Good, because pdflatex can be used
• Bad, because higher-quality typesetting is possible