# 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. 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 $a^j > a^i$.