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I have seen a similar post here How to remove the "." in the proof environment?. But I don't know how I can modify the answer to replace . with : by using etoolbox.

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You could use the easier way with the thmtools (see answer tex.stackexchange.com/a/31355/8042 ) by writing headpunct={:} – Ronny Feb 10 '12 at 8:33
up vote 7 down vote accepted

The easiest way to get Proof: (boldface italic) is to say

\renewcommand{\proofname}{\bfseries Proof:}

The \@addpunct command will not add its argument if it's preceded by a punctuation mark, so no change to the definition of the proof environment is necessary.

Note: the italic shape is already selected, so it's only necessary to add \bfseries. No braces are needed, as the heading is typeset as the optional argument to \item, which forms a group by itself.

One can, alternatively, patch the environment's definition in order to change \@addpunct{.} into \@addpunct{:} and to add \bfseries. Patching the environment with etoolbox is tricky, because the environment has an optional argument:


With the xpatch package it's easier:

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A very interesting fact about the \@addpunct command which I didn't know. – Thorsten Donig Feb 14 '12 at 19:06

Take the code for the proof environment from the sources of the amsthm package and modify it accordingly.

\usepackage{mathtools}   % loads »amsmath«

  \normalfont \topsep6\p@\@plus6\p@\relax

    This is a proof.
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Actually, I can remove the "." at the end as in the link I supplied above and redefine the proof name with a ":" at the end as follows. \def\proofname{\emph{\textbf{Proof:}}} But I find this no good. – bkarpuz Feb 10 '12 at 11:59
This is the way I do it when I want to change .->: or to change the font. – yo' Feb 10 '12 at 14:49
@bkarpuz. Do you understand this answer? I am completely confused. I find the other answer below more helpful and clear. – J G Feb 12 '12 at 6:29
@J G. I used the first one supplied in tex.stackexchange.com/a/44114/9955 by egreg. – bkarpuz Feb 13 '12 at 4:25
@bkarpuz: Then you should accept his answer and vote it up (if not done yet). – Thorsten Donig Feb 13 '12 at 18:50

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