How to start a list right after the heading in a redefined proof environment?

Question

I've redefined the proof environment to make the heading boldface by adapting the code from the amsthm documentation (p. 11). I've literally just deleted \itshape and typed \bfseries instead, nothing else was changed.

(Note: It doesn't even matter whether one changes the italics to boldface, the same problem arises when one copies the provided code from the documentation directly into the document.)

Unfortunately, lists now start on the second line instead of beginning right after the heading. Can this be fixed?

\documentclass[]{article}
\usepackage{amsthm, lipsum}

\makeatletter
\renewenvironment{proof}[1][\proofname]{\par
    \pushQED{\qed}%
    \normalfont \topsep6\p@\@plus6\p@\relax
    \trivlist
    \item\relax
    {\bfseries
        #1\@addpunct{.}}\hspace\labelsep\ignorespaces
}{%
\popQED\endtrivlist\@endpefalse
}
\makeatother

\begin{document}
\begin{proof}
    \begin{enumerate}
        \item \lipsum[66]
        \item \lipsum[66]
    \end{enumerate}
\end{proof}
\end{document}

Answer 1

You have two errors:

1. there should be [...] after \item, whereas you have {...}
2. \hskip\labelsep should go inside the optional argument

\makeatletter
\renewenvironment{proof}[1][\proofname]{\par
    \pushQED{\qed}%
    \normalfont \topsep6\p@\@plus6\p@\relax
    \trivlist
    \item[\hskip\labelsep\bfseries#1\@addpunct{.}]\ignorespaces
}{%
\popQED\endtrivlist\@endpefalse
}
\makeatother

Unfortunately, the code shown in the documentation is wrong. :(

Here is the original definition in amsthm.sty

\newenvironment{proof}[1][\proofname]{\par
  \pushQED{\qed}%
  \normalfont \topsep6\p@\@plus6\p@\relax
  \trivlist
  \item[\hskip\labelsep
        \itshape
    #1\@addpunct{.}]\ignorespaces
}{%
  \popQED\endtrivlist\@endpefalse
}

You might want to do

\usepackage{amsthm}
\usepackage{xpatch}

\xpatchcmd{\proof}{\itshape}{\bfseries}{}{}

that would avoid looking up the code.