# Theorem environment inside a footnote

I would like to write a theorem inside a footnote: the statement is not important in the main text, but I'd like to add it as a note. If I simply add a \begin{theorem} statement \end{theorem}, latex (correctly) adds a vertical space after the note number, but I'd like the head "Theorem" and the statement to be right after the number.

How can I do this? I tried with some negative vertical space in a \newtheoremstyle (see below), but it does not work, and I think there is a better solution than manually imitating it with \textbf and so on (as I did to create the last picture).

\newtheoremstyle{thminfootnote}
{-2cm} % Space above
{} % Space below
{} % Body font
{} % Indent amount
{.} % Punctuation after theorem head
{.5em} % Space after theorem head
{} % Theorem head spec (can be left empty, meaning normal')


I've done some research online, but I've managed to find just footnotes inside theorems or other environments, which is quite the opposite of what I'm looking for.

Here is my MWE (not working, actually), the screenshot of the PDF, and what i'd like.

\documentclass{article}

\usepackage{amsmath}
\newtheorem{theorem}{Theorem}

\begin{document}

By Pythagorean Theorem\footnote{
\begin{theorem}[Pythagoras's]
Given $a,b,c$ sides of a right triangle, we have $a^2+b^2=c^2$.
\end{theorem}} we can conclude that...

\end{document}


How it should be:

• If the theorem is not important enough to get to the main text, it is not important enough to be numbered. -> \footnote{Theorem Wombat: All Wombats are cuddly}. – Johannes_B Oct 29 '17 at 11:37
• Agree, in fact i'd use a theorem* in the real context. But I'd like to have the same layout. I've written only a MWE to explain the problem. – mattinodigitale Oct 29 '17 at 11:40
• Oh sorry, same format. \footnote{{\bfseries Theorem (Wombat)}\hspace{.5em}All Wombats are cuddly.} – Johannes_B Oct 29 '17 at 11:42
• An option could be Prevent a new line before a theorem, if you like a number after theorem you could use the old answer(see edit) – Bobyandbob Oct 29 '17 at 11:48
• Thanks @Johannes_B: I didn't know \hspace{.5em}. Of course this will work, i was wondering if there is a less "hand made" solution. For example, if i change something on the Theorem environment, i need to go and change it on this place too.. – mattinodigitale Oct 29 '17 at 11:48

Your readers will be very confused. Footnotes should only contain material that is not necessary for understanding the text; a theorem used in the proof of another theorem does not fall within this case, but opinions can differ.

\documentclass{article}
\usepackage{amsthm}

\newtheorem{theorem}{Theorem}

\makeatletter
\newenvironment{intexttheorem}[1][]
{%
\refstepcounter{theorem}%
\the\thm@bodyfont
}%
{\par}
\makeatother

\textheight=3cm % make a shorter picture

\begin{document}

By the Pythagorean Theorem\footnote{%
\begin{intexttheorem}[Pythagoras]
Given $a,b,c$ sides of a right triangle, we have $a^2+b^2=c^2$.
\end{intexttheorem}}
we can derive the following result.

\begin{theorem}[Cosine law]
Given $a,b,c$ sides of a triangle and $\gamma$ the opposite angle
to the side~$c$, we have $c^2=a^2+b^2-2ab\cos\gamma$.
\end{theorem}

\end{document}


If you have a \label, then it should be attached to the closing bracket of the optional argument or, without it, to the closing brace after intexttheorem.

• Do you really think footnote theorems should be numbered, inasmuch they're exceptional and outside of the general flow of theorems, propositions, &c.? – Bernard Oct 29 '17 at 12:41
• @egreg Thanks, this is precisely what i needed. Why do you think readers would be confused? I just want to produce a self-contained document, hence when I use quite-famous theorems inside a proof I'd like to put their statement somewhere. But, since they are not in the main topic, I think the footnote is a good place to put them into. Maybe an appendix would be a better, but for now i don't have enought of these "collateral" theorem to build one. – mattinodigitale Oct 29 '17 at 14:01
• @Bernard i won't number this footnote theorems, as you suggested. – mattinodigitale Oct 29 '17 at 14:02

This environment, obtained editing the one posted by @egreg above, seems to work perfectly (without the numbering, not touching the numbering flow of other theorem, and with the "(theorem name)" not in bold characters).

\makeatletter
\newenvironment{intexttheorem}[1][]
{%
`