Gettting rid of ntheorem's limitation concerning footnotes in theorem's notes

Question

As shown by the following MWE, footnotes in theorems' notes work well for amsthm's theorems:

\documentclass{article}
\usepackage{amsthm}
\newtheorem{theorem}{Theorem}
\begin{document}
\begin{theorem}[Foo\footnote{Bar.}]
Baz.
\end{theorem}
\end{document}

but, as shown by the following MNWE and according to this answer, not for ntheorem's theorems where the footnote texts are lost and the \footnotemark/\footnotetext trick is required:

\documentclass{article}
\usepackage{ntheorem}
\newtheorem{theorem}{Theorem}
\begin{document}
\begin{theorem}[Foo\footnote{Bar.}]
Baz.
\end{theorem}
\begin{theorem}[Foo\footnotemark]
  \footnotetext{Bar.}
Baz.
\end{theorem}
\end{document}

While it may not be a very good practice to put footnotes in theorem optional arguments, it could be useful in some cases, e.g. for citations in footnote as in the following MWE:

\documentclass{article}
\usepackage{amsthm}
% \usepackage{ntheorem}
\usepackage[backend=biber,style=authoryear]{biblatex}
\addbibresource{biblatex-examples.bib}
\newtheorem{theorem}{Theorem}
\begin{document}
\begin{theorem}[\citeauthor{knuth:ct}\footcite{knuth:ct}]
Baz.
\end{theorem}
\printbibliography
\end{document}

For some reasons, I'm stick to ntheorem and can't change it for amsthm. Any hope of a workaround to this ntheorem's limitation?

Answer 1

It is enough to load the footnote package and, thanks to its \makesavenoteenv command, to ask for the (ntheorem's) theorems to handle footnotes correctly:

\documentclass{article}
\usepackage{ntheorem}
\usepackage{footnote}
\usepackage[backend=biber,style=authoryear]{biblatex}
\addbibresource{biblatex-examples.bib}
\newtheorem{theorem}{Theorem}
\newtheorem{lemma}{Lemma}
\makesavenoteenv{theorem}
\makesavenoteenv{lemma}
\begin{document}
\begin{theorem}[\citeauthor{knuth:ct}\footcite{knuth:ct}]
Baz.
\end{theorem}
\begin{lemma}[\citeauthor{knuth:ct}\footcite{knuth:ct}]
Baz.
\end{lemma}
\printbibliography
\end{document}