Distance between text and footnote mark

Question

Sometimes I add footnotes to my proofs e.g. to specify where I took it from, such as in the following:

\documentclass{article}
\usepackage{amsthm}

\begin{document}

\begin{proof}[Proof\footnotemark]
\footnotetext{A footnote.}
The proof.
\end{proof}

\end{document}

If one were to typeset the above, one would find that the "f" of the word "Proof" collides with the footnote mark.

One could leave a space between the text and the footnote mark, but this would create too large a space between the text and the footnote mark.

I am puzzled as to why this should be a problem. The problem does not arise when one ordinarily writes italicised text.

Your help would be most highly appreciated.

Answer 1

The exact same effect can be seen in

\textit{Proof\footnotemark}

because the italic f leans to the right quite a bit and may intrude into other characters' space.

It is not visible, however, in

\textit{Proof}\footnotemark

because LaTeX inserts a so-called italic correction at the end of \textit to avoid such clashes.

You can insert the italic correction manually with \/

\documentclass{article}
\usepackage{amsthm}

\begin{document}

\begin{proof}[Proof\/\footnotemark]
\footnotetext{A footnote.}
The proof.
\end{proof}

\end{document}