# Why am I getting an undefined control sequence error in this line? [duplicate]

This line is giving me an error which I have been unable to remove for the last hour.

Let $a^i =p\times 10^{n+1} + r$ and $a^j =q\times 10^{n+1} + r$
be two such powers. Let $a^j \gt a^i$.

• MathJax has \lt and \gt because < and > might be confused with HTML tags; there's no such predefined command in LaTeX and Plain TeX. – egreg Apr 5 '16 at 6:29

Let $a^i =p\times 10^{n+1} + r$ and $a^j =q \times 10^{n+1} + r$
be two such powers. Let $a^j > a^i$.

• @user230452 where did you come across \gt I've not seen it? – Au101 Apr 5 '16 at 4:44
• @user230452 You are getting an undefined control sequence because the control sequence \gt has not been defined in your document class, or any of the packages that you load, or in some macro definition of your preamble. But you are always allowed to use it if you define what the hell \gt should do, e.g. \newcommand{\gt}{>} – Fran Apr 5 '16 at 4:56