Footnote within Intertext does not show (Align)

alignfootnotes

i am trying to finish up a Paper i am writing and used align with intertext in between, which made my footnote disappear. I tried using \footnotemark and \footnotetext after {align*}, this makes the footnote appear, but on the next page which is not really useful. How do i make it show up anyway? Help is very much appreciated, thanks in advance!

\usepackage{amsmath}  
\usepackage{amssymb}
\begin{document}
    
    Blabla:
    \begin{align*}
    X &= \bigcup\limits_{i=1}^{\infty} A^{-i} M. \\
    \intertext{Text inbetween}
        P_{1} &= S(A)M \cup M \cup X, \\
        P_{2} &= S(A^{-1})M \setminus X, \\
        P_{3} &= S(B)M, \\
        P_{4} &= S(B^{-1})M. \\
        Sodass: S^2\setminus D &= P_{1} \cup P_{2} \cup P_{3} \cup P_{4}.
        \intertext{Some more text with a helpful \footnote{I am helpful!}
        AP_{2} &= P_{2} \cup P_{3} \cup P_{4}, \\
        BP_{4} &= P_{1} \cup P_{2} \cup P_{4}.
        \intertext{last bit of text}
        S_{1} \sim (S^2\setminus D) &= P_{1} \cup AP_{2}, \\
        S_{2} \sim (S^2\setminus D) &= P_{3} \cup BP_{4}.
\end{align*}
\end{document}

Best Answer

\intertext adds a layer of boxing that prevents the footnote mechanism, but you can use the primitive \noalign

enter image description here

\documentclass{article}
\usepackage{amsmath}  
\usepackage{amssymb}
\begin{document}
    
    Blabla:
    \begin{align*}
    X &= \bigcup\limits_{i=1}^{\infty} A^{-i} M. \\
    \intertext{Text inbetween}
        P_{1} &= S(A)M \cup M \cup X, \\
        P_{2} &= S(A^{-1})M \setminus X, \\
        P_{3} &= S(B)M, \\
        P_{4} &= S(B^{-1})M. \\
        Sodass: S^2\setminus D &= P_{1} \cup P_{2} \cup P_{3} \cup P_{4}.
        \intertext{Some more text with a helpful\footnotemark}\noalign{\footnotetext{I am helpful!}}
        AP_{2} &= P_{2} \cup P_{3} \cup P_{4}, \\
        BP_{4} &= P_{1} \cup P_{2} \cup P_{4}.
        \intertext{last bit of text}
        S_{1} \sim (S^2\setminus D) &= P_{1} \cup AP_{2}, \\
        S_{2} \sim (S^2\setminus D) &= P_{3} \cup BP_{4}.
\end{align*}
\end{document}
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