The package provides macros for typesetting math formulas in
mixed horizontal and vertical mode, automatically as best fit.
It provides an environment mathpar that behaves much as a loose
centered paragraph where words are math formulas, and spaces
between them are larger and adjustable. It also provides a
macro \inferrule for typesetting fractions where both the
numerator and denominator may be sequences of formulas that
will be also typeset in a similar way. It can typically be used
for typesetting sets of type inference rules or typing
derivations. A macro inferrule for typesetting type inference
rules.

Homepage:
https://ctan.org/pkg/mathpartir
