This package extends the ifthen package by implementing new
commands to go within the first argument of \ifthenelse: to
test whether a string is void or not, if a command is defined
or equivalent to another. The package also enables use of
complex expressions as introduced by the package calc, together
with the ability of defining new commands to handle complex
tests. The package requires e-TeX features.

Homepage:
https://www.tug.org/texlive/
