# How to cite a proof

In my work I am giving a theorem and its proof from a book. I reproduce the proof and alter it slightly but obviously I need to tell the reader that I got it from that book. Where shall I do it? I don't want to say in my proof "This proof closely follows [1]" but need something more elegant that I can use on any other theorems. What is the standard/your favourite way to do this? Currently I alter to say: begin{proof}[Proof\cite{blah}] and then list my version.

Sorry if this is irrelevant...

I'd use something like you propose, maybe adding "from" or "see":

\begin{proof}[Proof (from {\cite[p.~25]{blah}})]
\begin{proof}[Proof (see {\cite[p.~25]{blah}})]


Maybe "from" if the proof is quoted verbatim and "see" if there is some change.

• Citation commands with a prefix/suffix need to be enclosed in braces {}. The Latin prefix "cf." could also be used to indicate that the proof is not simply a restatement of the cited result. – Audrey Apr 28 '11 at 17:00
• @user4483: Yes, of course. – egreg Apr 28 '11 at 17:02
• @egreg How could I change this if I wanted the source in P?roof (from {\cite{source}})'' to be unitalicized? – jdc Mar 31 '15 at 6:11
• @jdc Proof \textup{(from \cite{source})} – egreg Mar 31 '15 at 8:38
• Thank you (if it doesn't violate community standards to thank you in this box)! – jdc Mar 31 '15 at 19:17

If the theorem itself is also from the book, I would use

\begin{theorem}[Theorem 2.5 of~\cite{book}]


where "2.5" is of course the theorem number as it is typeset within the book. Alternatively, you could give a page number.

How this is typeset will depend on your bibliography style/citation format. For some formats this may look better:

\begin{theorem}[\cite[Theorem 2.5]{book}]