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.file extension IST - MakeIndex (TeX) style index
File extension IST description:
TeX is a typesetting system designed and mostly written by Donald Knuth. Together with the METAFONT language for font description and the Computer Modern typefaces, it was designed with two main goals in mind: to allow anybody to produce high-quality books using a reasonable amount of effort, and to provide a system that would give the exact same results on all computers, now and in the future. Within the typesetting system, its name is formatted as TeX.
TeX is considered by many to be the best way to typeset complex mathematical formulae. TeX is popular in academia, especially in the mathematics and physics communities. It has largely displaced Unix troff, the other favored formatter, in many Unix installations, which use both for different purposes. It is now also being used for many other typesetting tasks, especially in the form of LaTeX and other template packages.