# How may I discard the following error (undefined control sequence)?

Please note that this error does not affect for I could always ignore it and proceed, BUT I cannot figure out what causes it to occur. Error occurs at the last line; \end{flalign}

    \documentclass[11pt,a4paper]{article}
\usepackage{blindtext}
\usepackage{mathtools}
\DeclareMathOperator{\sgn}{sgn}
\begin{document}

\begin{flalign*}
+ba-ba&=
+b\times (+a-a)\\
&=(+a-a)\times (+b),\\
&=-b\times (+a-a),\\
&=(+a-a)\times (-b),\\
\end{flalign*}
\begin{flalign*}
&\unalign{\text{whence}}&& 0=(+b)\times 0=0\times (+b)=(-b)\times 0=0\times (-b);\\
&\unalign{\text {or briefly}}&& b\times 0=0\times b=0.
\end{flalign*}
\end{document}

• The problem is that there's no \unalign. What do you want to achieve with using that? Oct 23 '14 at 17:37
• If I did not write &\unalign{\text{whence}}&& 0=(+b)\times 0=0\times (+b)=(-b)\times 0=0\times (-b);\\ The word 'whence' and the symbolical statement would not be in the same line. If there is another way to achieve the same set up, I would like to try it without using \unalign. Oct 23 '14 at 17:44
• \unalign doesn't do anything other than generate an error, Oct 23 '14 at 18:01
• I should avoid the use of \unalign and rethink a way of getting the same set up by using a different environment. Thank you very much, David! This seems a mess. Oct 23 '14 at 18:16
• @NisalKevinKotinkaduwa you can just remove the command: it's doing nothing, if you are happy with the layout with it and the error, you should be happy with the layout without it and without the error, Oct 23 '14 at 20:01

Perhaps it is something like that you want?

\documentclass[11pt,a4paper]{article}
\usepackage{blindtext}
\usepackage{mathtools}
\DeclareMathOperator{\sgn}{sgn}
\begin{document}

\begin{flalign*}
+ba-ba& = +b × (+a-a)\\
& = (+a-a) × (+b),\\
& = -b × (+a-a),\\
& =(+a-a) × (-b),\\
\shortintertext{whence}
0 & =(+b) × 0=0 × (+b)=(-b) × 0=0 × (-b);\\
\shortintertext {or briefly}
& \begin{gathered} b × 0=0 × b=0. \end{gathered}
\end{flalign*}

\end{document}