I'm creating a Beamer presentation and whenever I try to compile, I get the 'Missing $ inserted' error and I have no idea why. I've looked at possible solutions to this problem but none have worked for me. The problematic section is the following:


With this very concrete characterization of the isotropy group of an algebraic theory $\mathbb{T}$ at hand, we can now compute the isotropy groups of several algebraic theories $\mathbb{T}$:



\item If $\mathbb{T}$ has no axioms, then the isotropy group of $\mathbb{T}$ is trivial, i.e. $\forall M \in \mathbb{T}mod$ we have $\mathcal{Z}_{\mathbb{T}}(M) = \{ [x] \} \cong 1$, the trivial group.


\item If $\mathbb{T}$ is the theory with one binary commutative or associative operation symbol, then the isotropy group of $\mathbb{T}$ is again trivial.


\item If $\mathbb{T}$ is the theory of groups, then Bergman essentially proved that $\forall G \in Group$ we have                $$ \mathcal{Z}_{\mathbb{T}}(G) = \{ [gxg^{-1}] \in G \langle x \rangle \: \mid g \in G \} \cong G. $$


\item If $\mathbb{T}$ is the theory of monoids, then $\forall M \in Monoid$ we have $$ \mathcal{Z}_{\mathbb{T}}(M) = \{[mxm'] \in M \langle x \rangle \mid \mbox{ m is invertible in M and m' = m^{-1} } \}. $$


I know that this section is the problem, because when I delete this section, the file is able to compile properly. Any help would be appreciated!

  • 4
    (1) It's much better to copy and paste the code instead of a screenshot. That way, we can copy and paste (and search) as well. (2) TeX error messages (while obtuse) generally point you in the right direction. What is it in this case? (3) I think mbox on the last item has its contents as text, so that any math inside should be in $. (4) You should use \[ and \] instead of $$. (5) Welcome to TeX.SE :)
    – Teepeemm
    May 31, 2018 at 21:11
  • 1
    If this section is indeed the problem, then you should be able to create a Minimal Working Example (MWE), starting with \documentclass{beamer}, \begin{document}, then this frame, and \end{document}. Can you confirm that the problem indeed occurs in that case? If yes, can you post the code for that so we can try it out (as also suggested by @Teepeemm)?
    – Marijn
    May 31, 2018 at 21:12
  • OK thanks, I will copy and paste it instead (sorry, first time asking a question on here).
    – User7819
    May 31, 2018 at 21:12
  • 1
    @User7819 and welcome to TeX.SE of course!
    – Marijn
    May 31, 2018 at 21:16
  • 1
    @User7819 See marked as a code sample May 31, 2018 at 21:26

1 Answer 1


you have error on the last item. correct is:

\item If $\mathbb{T}$ is the theory of monoids, then $\forall M \in Monoid$ we have 
        = \{[mxm'] \in M \langle x \rangle \mid \mbox{$m$ is invertible in $M$ and $m' = m^{-1}$} \}.

see changes in content of the mbox (it change it in text mode)

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