Cfrgtkky

I would like to be able to format my proof "like a horizontal tree". And because pictures are better than words, here is what I would like to do :

Proof :

To prove the big theorem, we first

need to prove that XXX:

| To prove XXX, let's begin to prove

| YYY:

| | YYY is trivial when you consider the

| | lemma 42, which is usable because of

| | the hypothesis 1.0. So YYY is true!

| Now, we would like also the property ZZZ

| Let's proove it !

| | To prove ZZZ, we can build a path and "paf !"

| | ZZZ becomes trivial !

| Let's now notice that applying YYY inside the

| | property YYY will let us conclude on the

| | validity of XXX.

□

So the idea is to indent the proof within several levels to always be clear about what we are proving, and show the indentation with a vertical border on the left. The result should looks like what you got when you enter in a While/If block within the algorithm2e package (but of course I don't want the If/While words):

Thank you for your help !

One solution I found is to use the mdframed package (very complete package and documentation !), and create a special box for that. Here is an example :

documentclass{article}

usepackage[utf8]{inputenc}

usepackage[T1]{fontenc}

usepackage[english]{babel}

usepackage{amsthm}

usepackage{thmtools}

usepackage{enumitem} % To avoid "Too deeply nested error"

usepackage{mdframed}



% For the subproof

newmdenv[linecolor=black

          ,topline=false

          ,bottomline=false

          ,rightline=false

          ,leftline=true

          ,leftmargin=0.1cm

          ,linewidth=0.02cm

          ,skipabove=0cm

          ,innerbottommargin=0.05cm

          ,skipbelow=0.05cm

          ]{subproof}

% Avoid alignement problem

setlength{parindent}{0cm}



% For the theorem environment

declaretheorem[name=Theorem]{theorem}



begin{document}



begin{theorem}[My great theorem]

  Hello, here is the best theorem ever

end{theorem}

begin{proof}

    Let's begin the proof !



    To prove the big theorem, we first need to prove XXX:

    begin{subproof}

      To prove XXX, let's begin to prove YYY:

      begin{subproof}

        YYY is trivial when you consider the lemma 42, which is usable because of the hypothesis 1.0. So YYY is true!

      end{subproof}

      Now, we would like also the property ZZZ

      Let's prove it !

      begin{subproof}

        To prove ZZZ, we can build a path and "paf !" ZZZ becomes trivial !

      end{subproof}

      Which ends the proof of XXX.

    end{subproof}

end{proof}

end{document}

Which gives :

Their is an alignment problem if you do not set setlength{parindent}{0cm}
(which I always do anyway). If you use one, I don't know if it's possible to detect if their is only one line in the above paragraph, so I would use two environments with one containing leftmargin=0.7cm...