# How to produce hollow Greek letters (in math mode)

I have a strange question regarding the notation of my thesis. My paper is on the topic of quantum algebra, so I have a plethora of symbols to sign to my definitions and defined functions. In a recent (yet brilliant) paper I found some very interesting symbols - hollow Greek letters. One of them looked like this:

And another one like this:

Or for example this beauty:

I don't know what packages were used to produce these symbols, but I started searching and soon found \usepackage[bbgreekl]{mathbbol} that produced the following result (code included):

\documentclass{article}

\usepackage{amsmath}
\usepackage{breqn}
\usepackage[bbgreekl]{mathbbol}
\usepackage{bbm}
%\usepackage[mtpbbi]{mtpro2}

\begin{document}

$\mathbb{A B \Gamma \Delta E Z H \Theta I K \Lambda M N \Xi O \Pi P \Sigma T \Upsilon \Phi X \Psi \Omega \alpha\beta\gamma\delta\epsilon\zeta\eta\theta\iota\kappa\lambda\mu\nu o \xi \pi\rho\sigma\tau\upsilon\phi\chi\psi\omega}$

\end{document}


This font is nice, don't get me wrong, but it isn't what I wanted to produce. I'd like my output to look exactly like the three symbols above. So I searched on. Note that one of my lines of code is commented with % and for a very good reason. I found another package that would output the hollow Greek letters. I don't know what font they are written in as my code didn't compile after I added \usepackage[mtpbbi]{mtpro2}. The following error showed up:

! LaTeX Error: File mtpro2.sty' not found.


I don't know what to do or if this package even offers what I'm searching for. I ask you (kind strangers) to show me a way to hollow the Greek letters so the three characters can be produced (alongside all other lower- and uppercase Greek letters, of course). Your help is much appreciated.

• If you want exactly those glyphs then do it like the paper's author did :-): good old \includegraphics... Jokes aside, mtpro2 is a commercial font which includes what they call "Holey Bold Italic" for greek letters: I can see only alpha, kappa and omega but it might be the correct font. Mar 24 '17 at 16:47

If pdf specials are an option then there is this approach. You can set the border color, fill color and border thickness (hat tip, Malipivo: TikZ: halo around text?).

\documentclass{article}
\usepackage{xcolor}
%%%
\makeatletter

%%% MALIPIVO's PDF SPECIAL TO CHANGE FONT OUTLINE THICKNESS/COLOR
% https://tex.stackexchange.com/questions/18472/tikz-halo-around-text/169549#169549
\input pdf-trans
\newbox\qbox
\def\usecolor#1{\csname\string\color@#1\endcsname\space}
\newcommand\bordercolor[1]{\colsplit{1}{#1}}
\newcommand\fillcolor[1]{\colsplit{0}{#1}}
\newcommand\outline[1]{\leavevmode%
\def\maltext{#1}%
\setbox\qbox=\hbox{\maltext}%
\boxgs{Q q 2 Tr \thickness\space w \fillcol\space \bordercol\space}{}%
\copy\qbox%
}
\makeatother
\newcommand\colsplit[2]{\colorlet{tmpcolor}{#2}\edef\tmp{\usecolor{tmpcolor}}%
\def\tmpB{}\expandafter\colsplithelp\tmp\relax%
\ifnum0=#1\relax\edef\fillcol{\tmpB}\else\edef\bordercol{\tmpC}\fi}
\def\colsplithelp#1#2 #3\relax{%
\edef\tmpB{\tmpB#1#2 }%
\ifnum #1>9\relax\def\tmpC{#3}\else\colsplithelp#3\relax\fi
}
\bordercolor{black}
\fillcolor{white}
\def\thickness{.3}
\begin{document}
\outline{This is a test $\eta \Lambda \nabla$}
\end{document}


• Wow, thanks! I see you are a pro at what you are doing (a LaTeX god, to be accurate). I appreciate your work and amazing skills at typesetting. You helped me very much. I just ask one small favor: the hollow lambda I exposed looks as if it was rendered using \mathbb command. The same goes for \nabla. Eta looks as if it was made bold first and then hollowed using the same method as you did (strangely enough?). If you know any CTAN package that would do these two things, please tell me about it. But the fact remains: you did an absolutely amazing job. Mar 24 '17 at 16:57
• @GregorPerčič I do not know a package to get exactly what you ask, but would note that different math fonts have different letter shapes. If you add \usepackage{mathptmx}, for example, to my MWE, it changes the math font globally, but in such a way that the symbols you mentioned come out clooking closer to (but still not the same as) the ones in your question. Mar 24 '17 at 17:08
• I experimented a bit and added \bm` so I made eta bold. Then this result came out (static.wixstatic.com/media/…). Surprisingly enough, it carries immense similarity to the original character. I can't thank you enough. Mar 24 '17 at 17:47