Latex \plus \times undefined in ACM template

Question

I am using an ACM template, and then I get the error Undefined control sequence for

\documentclass[sigconf]{acmart} 
\begin{document}
$(N[X],\plus,\times,0,1)$
\end{document}

I think it's caused by \plus and \times because after I removed them it works fine, but I don't know how to solve it.

Answer 1

The error message on the supplied document is

! Undefined control sequence.
l.3 $(N[X],\plus
                ,\times,0,1)$
? h
The control sequence at the end of the top line
of your error message was never \def'ed. If you have
misspelled it (e.g., `\hobx'), type `I' and the correct
spelling (e.g., `I\hbox'). Otherwise just continue,
and I'll forget about whatever was undefined.

? 

clearly showing that \plus is not defined. Use + to get a plus sign. (You would get the same error in the standard classes, not just ACM)