End Mark for Examples, Definitions and Theorems in LyX

Question

I'm using LyX and want to have an end mark for examples, definitions and theorems within chapters like this:

Theorem 1.1   Statement...... 
Definition 1.1   Statement...... 
Example 1.1   Statement...... 
Example 1.2   Statement...... 
Definition 1.2   Statement...... 

My LaTex preamble in LyX is:

\documentclass[12pt,oneside,english]{book}
\usepackage[T1]{fontenc}
\usepackage[latin9]{inputenc}
\usepackage{geometry}
\geometry{verbose,tmargin=4cm,bmargin=4cm,lmargin=4cm,rmargin=2cm}
\pagestyle{plain}
\setcounter{secnumdepth}{3}
\setcounter{tocdepth}{3}
\setlength{\parindent}{40bp}
\usepackage{color}
\usepackage{babel}
\usepackage{array}
\usepackage{bm}
\usepackage{multirow}
\usepackage{amsthm}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{setspace}
\usepackage[authoryear]{natbib}
\doublespacing
\usepackage[unicode=true,pdfusetitle,
 bookmarks=true,bookmarksnumbered=false,bookmarksopen=false,
 breaklinks=false,pdfborder={0 0 1},backref=false,colorlinks=true]
 {hyperref}
\hypersetup{
 linkcolor=black,citecolor=black,urlcolor=blue,filecolor=blue,pdfpagelayout=OneColumn,pdfnewwindow=true,pdfstartview=XYZ,plainpages=false,pdfpagelabels,citecolor=blue,linkcolor=blue}

\makeatletter

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% LyX specific LaTeX commands.
%% Because html converters don't know tabularnewline
\providecommand{\tabularnewline}{\\}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% Textclass specific LaTeX commands.
  \theoremstyle{definition}
  \ifx\thechapter\undefined
    \newtheorem{example}{\protect\examplename}
  \else
    \newtheorem{example}{\protect\examplename}[chapter]
  \fi
  \theoremstyle{plain}
  \ifx\thechapter\undefined
    \newtheorem{fact}{\protect\factname}
  \else
    \newtheorem{fact}{\protect\factname}[chapter]
  \fi
  \theoremstyle{definition}
  \ifx\thechapter\undefined
    \newtheorem{defn}{\protect\definitionname}
  \else
    \newtheorem{defn}{\protect\definitionname}[chapter]
  \fi
  \theoremstyle{plain}
  \ifx\thechapter\undefined
    \newtheorem{thm}{\protect\theoremname}
  \else
    \newtheorem{thm}{\protect\theoremname}[chapter]
  \fi

\@ifundefined{date}{}{\date{}}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% User specified LaTeX commands.
\usepackage[T1]{fontenc}
\usepackage{geometry}
\geometry{verbose,tmargin=3cm,bmargin=3cm,lmargin=3cm,rmargin=3cm}
\usepackage{babel}

\usepackage{hyperref}
\hypersetup{colorlinks=true,citecolor=blue, linkcolor=blue}
\usepackage{graphicx,epstopdf}
\usepackage{amsmath}
\usepackage[toc,page]{appendix}
\usepackage{bm}

\usepackage{tocloft,calc}
\renewcommand{\cftchappresnum}{Chapter } \AtBeginDocument{\addtolength\cftchapnumwidth{\widthof{\bfseries Chapter }}} 


\setlength{\cftafterloftitleskip}{12pt}  % list of figures
\setlength{\cftafterlottitleskip}{12pt}  % list of tables
\setlength{\cftaftertoctitleskip}{12pt}  % table of contents

\usepackage{titlesec}
\titlespacing*{\chapter}{0pt}{-50pt}{20pt}
\titleformat{\chapter}[display]{\normalfont\huge\bfseries}{\chaptertitlename\ \thechapter}{20pt}{\Huge}


\usepackage{tikz}
 \usetikzlibrary{matrix,decorations.pathreplacing, calc, positioning}

\usepackage{enumerate}

\usepackage[format=plain,labelfont=bf,up,textfont=it,up]{caption}

\usepackage{amssymb}
\usepackage{thmtools}
\declaretheorem[style=definition,qed=$\blacksquare$,numberwithin=chapter]{definition}

\makeatother

  \providecommand{\definitionname}{Definition}
  \providecommand{\examplename}{Example}
  \providecommand{\factname}{Fact}
\providecommand{\theoremname}{Theorem}

\begin{document}
Text

\end{document}

I would highly appreciate your help to figure out this problem. Thanks

Answer 1

Taking some guidance from Denoting the end of example/remark, use the following definitions for your theorem-like environments:

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% Textclass specific LaTeX commands.
  \theoremstyle{definition}
  \ifx\thechapter\undefined
    \newtheorem{examplex}{\protect\examplename}
  \else
    \newtheorem{examplex}{\protect\examplename}[chapter]
  \fi
  \newenvironment{example}
    {\pushQED{\qed}\renewcommand{\qedsymbol}{$\triangle$}\examplex}
    {\popQED\endexamplex}
  \theoremstyle{plain}
  \ifx\thechapter\undefined
    \newtheorem{factx}{\protect\factname}
  \else
    \newtheorem{factx}{\protect\factname}[chapter]
  \fi
  \newenvironment{fact}
    {\pushQED{\qed}\renewcommand{\qedsymbol}{$\blacksquare$}\factx}
    {\popQED\endfactx}
  \theoremstyle{definition}
  \ifx\thechapter\undefined
    \newtheorem{defnx}{\protect\definitionname}
  \else
    \newtheorem{defnx}{\protect\definitionname}[chapter]
  \fi
  \newenvironment{defn}
    {\pushQED{\qed}\renewcommand{\qedsymbol}{$\Box$}\defnx}
    {\popQED\enddefnx}
  \theoremstyle{plain}
  \ifx\thechapter\undefined
    \newtheorem{thmx}{\protect\theoremname}
  \else
    \newtheorem{thmx}{\protect\theoremname}[chapter]
  \fi
  \newenvironment{thm}
    {\pushQED{\qed}\renewcommand{\qedsymbol}{$\circ$}\thmx}
    {\popQED\endthmx}

Each theorem-like environment is defines using \newtheorem{<env>x} which defines the auxiliary environment <env>x, together with the main environment <env> which calls <env>x with appropriate QED-symbol (or end mark).

Using the above definitions, your end marks look like this:

\documentclass{book}
\usepackage{amsthm}% http://ctan.org/pkg/amsthm
\usepackage{amssymb}% http://ctan.org/pkg/amssymb

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% Textclass specific LaTeX commands.
\theoremstyle{definition}
\ifx\thechapter\undefined
  \newtheorem{examplex}{\protect\examplename}
\else
  \newtheorem{examplex}{\protect\examplename}[chapter]
\fi
\newenvironment{example}
  {\pushQED{\qed}\renewcommand{\qedsymbol}{$\triangle$}\examplex}
  {\popQED\endexamplex}
\theoremstyle{plain}
\ifx\thechapter\undefined
  \newtheorem{factx}{\protect\factname}
\else
  \newtheorem{factx}{\protect\factname}[chapter]
\fi
\newenvironment{fact}
  {\pushQED{\qed}\renewcommand{\qedsymbol}{$\blacksquare$}\factx}
  {\popQED\endfactx}
\theoremstyle{definition}
\ifx\thechapter\undefined
  \newtheorem{defnx}{\protect\definitionname}
\else
  \newtheorem{defnx}{\protect\definitionname}[chapter]
\fi
\newenvironment{defn}
  {\pushQED{\qed}\renewcommand{\qedsymbol}{$\Box$}\defnx}
  {\popQED\enddefnx}
\theoremstyle{plain}
\ifx\thechapter\undefined
  \newtheorem{thmx}{\protect\theoremname}
\else
  \newtheorem{thmx}{\protect\theoremname}[chapter]
\fi
\newenvironment{thm}
  {\pushQED{\qed}\renewcommand{\qedsymbol}{$\circ$}\thmx}
  {\popQED\endthmx}

\providecommand{\definitionname}{Definition}
\providecommand{\examplename}{Example}
\providecommand{\factname}{Fact}
\providecommand{\theoremname}{Theorem}

\begin{document}

\begin{example}Here is an example.\popQED\end{example}
\begin{fact}Here is a fact.\end{fact}
\begin{defn}Here is a definition.\end{defn}
\begin{thm}Here is a theorem.\end{thm}

\end{document}

---

Specific to LyX (2.0.4), set the document class to book:

followed by the inclusion of everything before \begin{document} in the LaTeX preamble:

Then, your LyX document:

---

On a completely different note: You need to clean up your LaTeX preamble... You're loading a number of packages more than once: fontenc, geometry, hyperref, ... This is just not necessary.