AtBeginEndPackage

First, obtain the style file from here: http://www-h.eng.cam.ac.uk/help/tpl/textprocessing/atbeginend.sty

Now install the style file (also see Cancel_Package#Using_Cancel_Package_in_LyX page on this wiki) by putting it into ~/Library/texmf/tex/latex (if you are on a Mac).

You may need to create this directory:

$ mkdir -p ~/Library/texmf/tex/latex

Now you should be able to fire up LyX and use it.

Open a document, click Document > Settings..., and in the preamble, put

\renewcommand{\labelenumi}{\LARGE \textbf{\arabic{enumi}.}} \renewcommand{\labelenumii}{\normalsize \textbf{\arabic{enumi}.\arabic{enumii}.}} \renewcommand{\labelenumiii}{\normalsize \textbf{\arabic{enumi}.\arabic{enumii}.\arabic{enumiii}.}} %% the following according to http://www.eng.cam.ac.uk/help/tpl/textprocessing/squeeze.html %% add some space: \usepackage{atbeginend} \AfterBegin{itemize}{%

 \addtolength{\itemsep}{0.9\baselineskip}%

} \AfterBegin{enumerate}{%

 \addtolength{\itemsep}{0.9\baselineskip}%

}