I'm sorry because there are already a lot of questions on this site with such a title but no one seems to have the same problem as I have. I'm new to LaTeX and to this forum by the way. Here is my issue: without the align* environment, I get no errors, but when I want to align all my lines and use align*, I get "! Missing } inserted. } l.154 \end{align*}"
How to align all my "=" then? My code is just below. Thank you in advance for you feedback.
\begin{align*}
Ker(\psi) &= \{ (\sigma, e) \in \mathfrak A_{n} \rtimes_{\varphi} \{-1, 1\}, \psi(\sigma, e)=~$id$_{\mathfrak S_{n}} \} \\
&= \{ (\sigma, e) \in \mathfrak A_{n} \rtimes_{\varphi} \{-1, 1\}, i(\sigma)s(e)=~$id$_{\mathfrak S_{n}} \} \\
&= \{ (\sigma, e) \in \mathfrak A_{n} \rtimes_{\varphi} \{-1, 1\}, i(\sigma)s(e)=~$id$_{\mathfrak S_{n}} \} \\
&= \{ (\sigma, e) \in \mathfrak A_{n} \rtimes_{\varphi} \{-1, 1\}, i(\sigma)=~$id$_{\mathfrak S_{n}}~$et$~s(e)=~$id$_{\mathfrak S_{n}} \} \\
&= \{ ($id$_{\mathfrak A_{n}}, 1) \}
\end{align*}