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I was writing up a proof on a LaTex article, which required me to utilise a number of matrices in it.

However, I quickly discovered that when I hit \end{proof}, at the end of my proof, it would not register as the end of my proof, or even recognise the proof command, thus not including the end proof box, and I quickly noticed that even the beginning proof. had disappeared.

I experimented with other options: Putting the begin{proof} and end{proof} on either side of a paragraph with no matrices seemed to work fine. But the moment I added a matrix using the following code, I ran into a problem:

4. Two columns/rows of the matrix are identical. This is simply a property of a matrix.
\begin{Proof}
  Let us say we have an n x n matrix A, shown below:
  \[
  \begin{bmatrix}
    $a_{11}$ & $a_{12}$ & $a_{13}$ & ... & $a_{1n}$\\
    $a_{21}$ & $a_{22}$&... &... &$a_{2n}$ \\
    $a_{i1}$ & ...&... &... &$a_{in}$ \\
    $a_{n1}$ & ...&... &... &$a_{nn}$ \\
  \end {bmatrix}\\
  \]
  \end{Proof}

It shows up like this:

Where is the proof?

With no proof.

It is not a problem with my packages, I have used proofs successfully throughout the document, and here is my preamble:

\documentclass{article}
\usepackage{amsthm}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage[margin=1.25in]{geometry}
\usepackage[shortlabels]{enumitem}
\usepackage{graphicx}
\usepackage{fancyhdr}
\renewcommand{\headrulewidth}{0pt}
\renewcommand{\footrulewidth}{1pt}
\fancyhfoffset{0.2cm}
\pagestyle{fancy}
\rfoot{redacted}
\addtolength{\footskip}{0.2in}
\newtheorem*{theorem}{\sc{Theorem}}
\newtheorem*{definition}{\sc{Definition}}
\newtheorem*{proposition}{\sc{Proposition}}
\newtheorem*{corollary}{\sc{Corollary}}
\newtheorem*{claim}{\sc{Claim}}
\newtheorem*{properties}{\sc{Properties}}
\newtheorem*{remark}{\sc{Remark}}
\DeclareMathOperator{\N}{\mathbb{N}}
\DeclareMathOperator{\Z}{\mathbb{Z}}
\DeclareMathOperator{\Q}{\mathbb{Q}}
\DeclareMathOperator{\R}{\mathbb{R}}
\DeclareMathOperator{\C}{\mathbb{C}}

Any ideas why this is happening and what I can do to fix it?

  • How or where is the Proof environment defined? – Mico Jun 26 at 6:40
  • It is defined as I have used it on multiple occasions throughout the document and it has worked. Only difference is the matrix – global05 Jun 26 at 6:41
  • Incidentally, \sc is a "switch", i.e., it doesn't take an argument. You should write either \textsc{...} or {\scshape ...}. – Mico Jun 26 at 6:42
  • I see: You have a typo in your code: \begin{Proof} should be \begin{proof}. Also, all 22 [!] instances of $ inside the bmatrix environment have to be deleted. Once you fix these issues, the end-of-proof symbol shows up. – Mico Jun 26 at 6:43
3

You have a basic typo in your code: The amsthm package defines an environment called proof, but not one called Proof.

If you use \begin{Proof} and \end{Proof}, and if you choose to ignore plenty of LaTeX warning messages, you'll eventually obtain the following output:

enter image description here

Indeed, no "Proof" label up front, and no end-of-proof symbol at the end.

Happily, once you change \begin{Proof} and \end{Proof} to \begin{proof} and \end{proof}, respectively, you'll get the following output:

enter image description here

Moral of the story: Never, ever ignore LaTeX's warning messages.

(PS To make your code compile, I also had to delete all 22 instances of $ inside the bmatrix environment.)

\documentclass{article}
\usepackage{amsthm,amsmath}
\usepackage[margin=1.25in]{geometry}
\usepackage[shortlabels]{enumitem}

\begin{document}
\begin{enumerate} \setcounter{enumi}{3} % just for this example
\item Two columns/rows of the matrix are identical. This is simply a property of a matrix.
\begin{Proof} % <-- typo
  Let us say we have an $n \times n$ matrix $A$, shown below:
  \[
  \begin{bmatrix}
    a_{11} & a_{12} & a_{13} & ... & a_{1n} \\
    a_{21} & a_{22} &...     & ... & a_{2n} \\
    a_{i1} & ...    &...     & ... & a_{in} \\
    a_{n1} & ...    &...     & ... & a_{nn} 
  \end{bmatrix} 
  \qedhere % optional
  \]
  \end{Proof} % <-- typo
\end{enumerate}
\end{document}
| improve this answer | |
  • You marked the typos but I think you forgot to correct them ;-) – campa Jun 26 at 7:20
  • 1
    Ah, the attention to detail. This worked. – global05 Jun 26 at 7:43
  • @campa - Fixing the very last few details is left as an exercise to the readers, right? (I did eliminate all 2*11=22 [!] spurious $ symbols…) – Mico Jun 26 at 8:59

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