# Undefined control sequence undetectable [closed]

I came across the following error message:

! Undefined control sequence.
l.206 ...quad a_k > \displaystyle\sum_{{\substrack
{j=1 \\ j \neq k}}}^N\disp...


Pardon my ignorance.

• Read the FAQ entry How do I ask questions here? for guidance on voting and accepting answers.
– Werner
Jan 24, 2012 at 6:59
• It would be helpful if, in your posting, you only included the error message and left out the (at this point) meaningless LaTeX warnings.
– Mico
Jan 24, 2012 at 7:11

You are looking for the command \substack not \substrack.

• Thak's for everyone and specially for Werner. After correction, I still have this error message: ! Undefined control sequence. l.206 ...\quad a_k > \displaystyle\sum_{{\substack {j=1 \\ j \neq k}}}^N\disp.. Jan 24, 2012 at 11:42
• @Labaïr If you have an error message, why not edit the question showing what you did and the error message? Jan 24, 2012 at 15:03
• Now i have this message: ! LaTeX Error: Environment remarques undefined. See the LaTeX manual or LaTeX Companion for explanation. Type H <return> for immediate help. ... l.396 \begin{remarques} Jan 24, 2012 at 15:04
• @Labaïr: The remarques environment is not defined. But this could be a host of things. For example, if it should be a "theorem" or a regular environment. You need to post more information.
– Werner
Jan 24, 2012 at 15:20

\substack is defined in the amsmath package, you need to load that package (or one of the ams classes that includes it)

• Now I have this message:! LaTeX Error: Environment remarques undefined. See the LaTeX manual or LaTeX Companion for explanation. Type H <return> for immediate help. ... l.396 \begin{remarques} Jan 24, 2012 at 15:06
• so clearly you need to load whatever package defines that. i have never used it but lmgtfy.com/?q=latex+remarques shows some hits Jan 24, 2012 at 15:30
• I write \newenvironment{remark}[1][\textbf{Remarques:}]{\begin{trivlist} \item[\hskip \labelsep {\bfseries #1}]}{\end{trivlist}} with the package ntheorem Jan 24, 2012 at 15:43
• I'm really surprised that after you are able to ignore the crowd of people who ask you to be fair and accept the answers to your questions. To your issue: Your environment is obviously named remark and not remarque.
– yo'
Jan 24, 2012 at 16:00
• I would like to extend my apologies to all people in this post. Jan 24, 2012 at 17:06