Sstrhsrtj

I would like to be able to recreate the following theorem style, where the main body of a theorem/proof/definition etc. is indented by a variable amount. I would also like to end a theorem proof with a filled circle rather than a square. The labels "Definition 1.1., etc." should be vertically aligned with the first line of the definition text. How do I go about achieving this?

As a starting point, I am working with the following document.

documentclass[11pt,a4paper]{article}

usepackage[margin=2.5cm]{geometry}

usepackage{xcolor}

usepackage[calcwidth]{titlesec}

usepackage{blindtext}

usepackage{scrextend}

usepackage{microtype}

usepackage[leqno]{amsmath}

usepackage[standard,amsmath,thmmarks]{ntheorem} 

usepackage{etoolbox}

makeatletter

setlength labelsep {3.15em} 

newtheoremstyle{mymargin}%

{item[theorem@headerfont llap{##1 ##2}]}%

{item[theorem@headerfont llap{##1 ##2}| ##3theorem@separatorhskiplabelsep]}%

makeatother





% my definition

theoremstyle{mymargin}

theorembodyfont{}   

theoremsymbol{}

theoremprework{}

theorempostwork{}

theoremseparator{.}

newtheorem{mydefinition}{Definition}

numberwithin{mydefinition}{section}

newtheorem{mythm}{Theorem}

numberwithin{mythm}{section}



begin{document}



section{A test section}

begin{addmargin}[10em]{0em}begin{mydefinition}blindtextend{mydefinition}

end{addmargin}



end{document}

I don't like ntheorem. Here's a modification of https://tex.stackexchange.com/a/106582/4427

documentclass[a4paper]{article}

usepackage{amsthm,thmtools}

usepackage{etoolbox}



usepackage{lipsum} % just for context

usepackage{showframe} % for showing the margins



makeatletter

newlength{thmindent}

AtBeginDocument{setlength{thmindent}{15em}}

patchcmd@thm

  {trivlist}

  {list{}{leftmarginthmindent}}

  {}{}

newcommand{xdeclaretheorem}[2]{%

  declaretheorem[#1]{#2}%

  expandafterpatchcmdcsname thmt@original@end#2endcsname

    {endtrivlist}{endlist}{}{}%

}



renewenvironment{proof}[1][proofname]{par

  pushQED{qed}%

  normalfont 

  list{}{leftmargin=thmindent}

  item

  makebox[0pt][r]{makebox[thmindent][l]{itshape#1@addpunct{.}}}ignorespaces

}{%

  popQEDendlist@endpefalse

}

renewcommand{qedsymbol}{textbullet}

makeatother





declaretheoremstyle[

  headpunct={},

  headfont=bfseries,

  bodyfont=normalfont,

  headindent=0pt,

  postheadspace=0pt,

  headformat={makebox[0pt][r]{makebox[thmindent][l]{NAME NUMBER.}}},

]{INDENTthm}



xdeclaretheorem[

  within=section,

  style=INDENTthm,

  name=Theorem

]{thm}



xdeclaretheorem[

  sibling=thm,

  style=INDENTthm,

  name=Lemma

]{lem}



begin{document}



begin{thm}

lipsum*[2]

begin{enumerate}

item a

item b

end{enumerate}

end{thm}



begin{lem}

lipsum*[2]

begin{enumerate}

item a

item b

end{enumerate}

end{lem}



begin{proof}

lipsum*[2]

end{proof}



end{document}