# Undefined control sequence \IfFormatAtLeastTF

I am using `\RequirePackage{expkv/expkv-opt,expkv/expkv-def}` in my `sty` file. But when I run my `tex` file I am getting the following error.

``````This is pdfTeX, Version 3.14159265-2.6-1.40.18 (TeX Live 2017/Debian) (preloaded format=pdflatex)
restricted \write18 enabled.
entering extended mode
LaTeX2e <2017-04-15>
Babel <3.18> and hyphenation patterns for 84 language(s) loaded.

Document Class: book 2014/09/29 v1.4h Standard LaTeX document class
(/usr/share/texlive/texmf-dist/tex/latex/base/bk10.clo))
(/home/Opstk/vulcan-kmpj/expkv/expkv-opt
.sty
/home/Opstk/vulcan-kmpj/expkv/expkv-opt.
sty:34: Undefined control sequence.
l.34 \IfFormatAtLeastTF
{2021/05/01}
?
/home/Opstk/vulcan-kmpj/expkv/expkv-opt.
sty:34: Emergency stop.
l.34 \IfFormatAtLeastTF
{2021/05/01}
/home/Opstk/vulcan-kmpj/expkv/expkv-opt.
sty:34:  ==> Fatal error occurred, no output PDF file produced!
Transcript written on fredholm.log.
/usr/local/bin/texi2dvi: pdflatex exited with bad status, quitting.

Compilation exited abnormally with code 1 at Tue Apr 26 13:13:19
``````
• You omitted the part of the log which would have given the answer, the latex version banner given at the start of every run. Apr 26 at 7:17

The `\IfFormatAtLeastTF` built-in was introduced for the October 2020 release. That you have an undefined control sequence means that you are running on an older kernel.
• Or you can add `\providecommand\IfFormatAtLeastTF{\@ifl@t@r\fmtversion}` to the document. It is recommended that package authors add this to their package before using `\IfFormatAtLeastTF` if they want compatibility with older LaTeX releases (at least for some time, until LaTeX releases older than 2020-10-01 are nearly extinct) Apr 26 at 1:42
• Am also getting a problem with `\DeclareRelease`. Apr 26 at 1:50
• Same comment as above; but `\DeclareRelease` was introduced in 2017. So you have a very old TeX kernel running. You absolutely should update your TeX installation to something significantly more current. @Ephram Are you actually using a TeX installation from 2015 ish? Apr 26 at 3:09
• Quite right. I have `This is pdfTeX, Version 3.14159265-2.6-1.40.18 (TeX Live 2017/Debian) (preloaded format=pdflatex) restricted \write18 enabled.` Apr 26 at 12:55