2

I want

\newtheorem*{prf}{\normalfont\scshape Proof}

but with an automatic \qedsymbol at the end (QED).

2
  • You want the proof to end with the acronym QED? (or maybe EOΔ ?)
    – Bernard
    Commented Aug 30, 2020 at 13:48
  • @Bernard sorry it took so long to get back to you, I want the acronym QED
    – user716881
    Commented Aug 31, 2020 at 6:47

2 Answers 2

2

Here is a way to do this with ntheorem:

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{fourier}
\usepackage[svgnames]{xcolor}

 \usepackage{amsmath, amssymb}
\usepackage[thmmarks, amsmath, thref]{ntheorem}

\theoremstyle{plain}
\theoremheaderfont{\upshape\bfseries}
\theoremseparator{.}
\theorembodyfont{\itshape}
\newtheorem{thm}{Theorem}


\theoremstyle{nonumberplain}
\theoremheaderfont{\scshape}
\theoremseparator{:}
\theorembodyfont{\upshape}
\theoremsymbol{\ensuremath{\color{Gainsboro}\blacksquare}}
\newtheorem{prf}{Proof}

\begin{document}

\begin{thm}\label{th-a}
This theorem is awesome!
\end{thm}

\begin{prf}
One-lined proof: Blahblah Blahblah Blahblah.
\end{prf}

\begin{prf}[Variant]
This is a very important proof.
\begin{align*}
    a & = b\\ c & = d.
\end{align*}
\end{prf}

\end{document} 

enter image description here

1
  • I wrote \usepackage[thmmarks, amsmath, thref]{ntheorem} \theoremstyle{nonumberplain} \theoremheaderfont{\scshape} \theoremseperator{:} \theorembodyfont{\upshape} \theoremsymbol{QED} \newtheorem{prf}{Proof} ````` and I got ! Package ntheorem Error: Theorem style plain already defined. ! LaTeX Error: Environment equation* undefined. ! Undefined control sequence.````
    – user716881
    Commented Aug 31, 2020 at 6:41
2

It can be done with the usual proof environment of amsthm. It has an optional argument to set the name of the proof, so you can also pass \normalfont\scshape to this argument to set the font.

\documentclass[11pt]{article}
\usepackage{amsthm}
\newtheorem*{thm}{Theorem}
\newenvironment{prf}[1][Proof]{%
    \begin{proof}[\normalfont\scshape #1]%
}{%
    \end{proof}%
}
\begin{document}
\begin{thm}
A theorem.
\end{thm}
\begin{prf}
The proof.
\end{prf}
\end{document}

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