# How can I typeset a blackboard bold number in amstex?

I'm using plain TeX with AmsTeX. I can get blackboard bold capital letters, but not numbers. For example, the command \Bbb A prints a capital blackboard bold letter A, but the command \Bbb 1 displays a strange symbol which, of course, is not a blackboard bold number.

• The blackboard bold characters available in the msbm fonts are for the uppercase letters and the lowercase k. – egreg Apr 1 '15 at 14:43
• amstex? a strange choice this century! Why not use a supported format? – David Carlisle Apr 1 '15 at 15:12
• @DavidCarlisle I use AmsTeX because is the only reasonable format I found which adds support for typesetting math and is compatible with plain TeX. I once gave LaTeX a change, but I found it to be more complicated for doing simple things and personally I don't like it's philosophy (maybe this is because I learnt TeX through The TeXBook and The Joy of TeX). If I need more advanced LaTeX-like features such as cross-referencing or automatic index and table of contents creation, I use the macros in eplain. So I think I'm not missing anything by using this old unsupported format. Don't you agree? – User Apr 1 '15 at 18:57
• Document creation is a form of communication and ultimately using a language that no one, not even its creators, use anymore, is a completely bizarre choice unless there is an overwhelming large corpus of existing documents that you can not afford to convert. – David Carlisle Apr 1 '15 at 19:07
• @DavidCarlisle "not even its creators" Michael Spivak still uses AmsTeX (to be precise, he uses LamsTeX which extends AmsTeX). Anyway, I understand your point of view. By the way, even in the opmac documentation (which I just looked at, thank's to the answer of wipet) amstex is mentioned and it is explained how to properly use opmac alongside amstex. So I don't think it is so old and unused – User Apr 1 '15 at 21:05

The msbm font has only blackboard bold uppercase letters and the lowercase k.

If you want digits, you have to use another blackboard bold font.

Here's the code for bbold

\input amstex

\catcode@=11
\font@\tenbbold=bbold10
\font@\sevenbbold=bbold7
\font@\fivebbold=bbold5
\newfam\bboldfam
\textfont\bboldfam=\tenbbold
\scriptfont\bboldfam=\sevenbbold
\scriptscriptfont\bboldfam=\fivebbold
\def\xbb{\RIfM@\expandafter\xbb@\else
\expandafter\nonmatherr@\expandafter\xbb\fi}
\def\xbb@#1{{\xbb@@{#1}}}
\def\xbb@@#1{\noaccents@\fam\bboldfam\relax#1}

\catcode@=\active % @ is active in amstex

$\Bbb{A}\xbb{0123456789}$

\bye


In plain TeX, you can use OPmac:

\input opmac

%% adding math family for bbold fonts:
\regtfm bbold 0 bbold5 5.5 bbold6 6.5 bbold7 7.5 bbold8 8.5 bbold9 9.5
bbold10 11.1 bbold12 15 bbold17 *
\def\xbbchar{\fam15 }

Ten points: $\bbchar ABCDEF_G$, $\xbbchar 01234_5$.

\typosize[12/14] Twelve points:  $\bbchar ABCDEF_G$, $\xbbchar 01234_5$.

\end


You can see, that simple font-size changing is possible:

When OPmac is loaded then all math symbols from AMS TeX are available. This implies that there is no need to load amstex.tex explicitly. But you can do this, of course. If you do this, then I recommend first to load amstex.tex and second opmac.tex. The second file re-defines the font settings and math symbols to more intelligent way.

Edit: I've added the loading of the new font family bbold* using OPmac because OP needs the bbchars for digits. The new math font selector \xbbchar is declared. The font-size changing is working too. Note, that the \regtfm is used here because we have more optical sizes of bbold*.tfm files: 5, 6, 7, 8, 9, 10, 12 and 17.

• But then $\bbchar 123$ gives the problem the OP was trying to avoid. – Manuel Apr 1 '15 at 16:02
• @Manuel Thank you for your comment. I've updated my post. – wipet Apr 1 '15 at 16:52
• Of course this is not fully compatible with AMSTeX, as it doesn't use \font@. Why \fam15? Can't OPMac use \newfam instead of explicit numbers? – egreg Apr 1 '15 at 18:21
• @egreg OPmac allocates fam0 to fam13. The fam14 and fam15 are in "user space". There is no more fams in classical TeX. OPmac documentation recommends to users to choose between 14 and 15 directly. Of course, if we are using a TeX extension with more than 16 fams then \newfam allocator has its sense. – wipet Apr 1 '15 at 18:56
• @wipet Thank's for having pointed me out the OPmac format. It seems really interesting :) – User Apr 1 '15 at 19:01