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I want to define a simple environment to enclose my proofs, actually I just wanted to put a little square right at the end. So, I made this new environment definition:

\newenvironment{Proof}{ \flushleft \textbf{PROOF}}{\rule{1ex}{1ex}}

When I use this environment to enclose simple text, then I get the little square right at the end, after the last character. The problem is when I enclose an enumerate environment because it adds a new line and put the little square at the beginning. In this case my problem is both I don't want the new line and also I need the square at the right ending of the margin. If I consider it this way

\newenvironment{Proof}{ \flushleft \textbf{PROOF}}{\begin{flushright} \rule{1ex}{1ex} \end{flushright}}

then a new line is always added.

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I would consider doing what barbara suggests, there's a well-done proof environment. You suggest using a black box (\rule{1ex}{1ex}), this can be achieved too, by redefining \qedsymbol. – yo' Feb 7 '13 at 20:23
up vote 7 down vote accepted

amsthm automatically puts a box (an open box, but that can be redefined) flush right at the end of the last line of proof. if the proof ends with a display or a list, then \qedhere can be used just before the end of that environment to move the box to the proper line.

to start the enumerated list on a new line after the proof header, enter it as


documentation is available with texdoc amsthm (if you are using a system based on tex live) or by visiting the page and clicking on the line "AMS theorem package user's guide".

to redefine the qed box,


to change the main proof header,


(thanks, egreg.)

for a one-time variant, just take advantage of the optional argument:

\begin{proof}[Proof of the XYZ theorem}
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Great! how can exactly redefine the box? – Daniela Diaz Feb 7 '13 at 20:25
Perfect!. Just a last question, sorry because I'm so new on this. How can I change the format of word "proof". – Daniela Diaz Feb 7 '13 at 20:44
@DanielaDiaz \renewcommand{\proofname}{Whatever} if you don't use babel. If you use babel with language spanish (just as an example), \addto\captionsspanish{\renewcommand{\proofname}{Whatever}} – egreg Feb 7 '13 at 21:05

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