# mathbb-one

`\mathbb{1}` for amssymb.

amssymb's blackboard bold has no digits, so `\mathbb{1}` prints a stray symbol instead of
the indicator 𝟙. mathbb-one adds the missing 1 and changes nothing else:

```latex
\usepackage{amssymb}
\usepackage{mathbb-one}

$\mathbb{E}[\mathbb{1}_A] = \mathbb{P}(A)$
```

The glyph is the 1 from Gilles F. Robert's bbm fonts, the usual choice for an indicator
because it matches the Computer Modern style of `\mathbb`. bbm only exists as Metafont
source, so pdfLaTeX embeds it as a 600 dpi bitmap. mathbb-one ships it as a Type 1 outline
font instead.

![bbm bitmap (left) and mathbb-one (right), enlarged](doc/img/zoom.png)

## Compared with the alternatives

Every answer to [TeX.SE question 26637](https://tex.stackexchange.com/q/26637), each set
the way the answer suggests. Packages that replace `\mathbb` also change the letters
next to the 1.

![blackboard-bold 1 options](doc/img/alternatives.png)

## Details

- Works with pdfLaTeX, LuaLaTeX and XeLaTeX. Load it before or after amssymb.
- `\mathbb{1}` works in subscripts and next to letters (`\mathbb{R1}`). Other
  `\mathbb` letters and ordinary digits are not affected.
- `\Bbbone` is also defined, under the same name unicode-math uses. If unicode-math is
  loaded, mathbb-one does nothing and the math font's own 𝟙 is used.
- Sizes follow amssymb: one design each for 5pt, 7pt and 10pt and up. So the 1 has the
  same weight relative to the letters as `\mathbb` does, in text and in subscripts.
- mathbb-one doesn't need bbm or bbm-macros.

## OpenType version

If you use LuaLaTeX or XeLaTeX with unicode-math, your math font already has a 𝟙.
If you'd rather have bbm's, `opentype/mathbb-one.otf` provides just that glyph.
Don't load mathbb-one.sty; take the 1 from the OpenType font instead:

```latex
\usepackage{unicode-math}
\setmathfont{NewCMMath-Regular.otf}
\setmathfont[range="1D7D9]{mathbb-one.otf}   % 𝟙 (U+1D7D9) comes from mathbb-one
```

This changes `\Bbbone`. unicode-math sets `\mathbb{1}` through its blackboard-digit
alphabet instead, so if you write `\mathbb{1}`, use `range={"1D7D9,bb/num}`. The catch is
that `\mathbb{0}`, `\mathbb{2}`, ... then come out empty, because the font only has the 1.

XeLaTeX finds fonts by file name only if you write the `.otf` extension, as above.

## Install

**From TeX Live or MiKTeX** (once mathbb-one is on CTAN): nothing to do, just
`\usepackage{mathbb-one}`. If it's missing, run `tlmgr install mathbb-one` or use the MiKTeX
console.

**In a single project** (also Overleaf, or a journal submission): put these files
**flat in the same folder as your main `.tex` file**, not in a subfolder:

```
paper.tex
mathbb-one.sty
mathbb-one.map
mathbb-one5.tfm  mathbb-one7.tfm  mathbb-one10.tfm
mathbb-one5.pfb  mathbb-one7.pfb  mathbb-one10.pfb
```

They're in this repo's `tex/`, `map/`, `tfm/` and `type1/` folders, and in the same folders of
`mathbb-one.zip` from the
[releases](https://github.com/t-a-beck/mathbb-one/releases). TeX finds them by name in the
document's folder, but it doesn't search subfolders.

To keep them in a subfolder instead, say `mathbb-one/`, add a file named `latexmkrc` next to
your `.tex` file:

```perl
# Let TeX find mathbb-one's files in the mathbb-one/ subfolder.
foreach my $var ('TEXINPUTS', 'TFMFONTS', 'T1FONTS', 'TEXFONTMAPS') {
    ensure_path($var, './mathbb-one//');
}
```

This works when you build with `latexmk` (also via the LaTeX Workshop extension in
VS Code, and on Overleaf, which reads a `latexmkrc` in the project root).

**For all your documents:** run `make install`. It copies the files into your personal
TeX tree (`TEXMFHOME`, usually `~/Library/texmf` on macOS or `~/texmf` on Linux), where
they have to sit in the standard layout. To do it by hand, copy this repo's folders as follows:

| This repo | Into `TEXMFHOME` |
|---|---|
| `tex/` | `tex/latex/mathbb-one/` |
| `tfm/` | `fonts/tfm/public/mathbb-one/` |
| `type1/` | `fonts/type1/public/mathbb-one/` |
| `map/` | `fonts/map/dvips/mathbb-one/` |
| `opentype/` | `fonts/opentype/public/mathbb-one/` |

You don't need to run `updmap`
or `mktexlsr`. `make uninstall` removes the files again.

## Building the fonts

```sh
brew install potrace fontforge
make fonts
```

`source/build.sh` renders the 1 of `bbm5`, `bbm7` and `bbm10` at high resolution with
Metafont, traces it with potrace, and assembles a one-glyph `.pfb` with FontForge.
`pk2pbm.py` needs only the Python standard library. `build_t1.py` runs inside FontForge's
own Python. Run it from a path without spaces, because Metafont can't read them.

`make doc` rebuilds the user guide [doc/mathbb-one.pdf](doc/mathbb-one.pdf) and the comparison sheet
[doc/mathbb-one-compare.pdf](doc/mathbb-one-compare.pdf). `make ctan` builds `mathbb-one.zip`, the CTAN
upload.
`make release VERSION=x.y` builds that zip, tags `vx.y` and publishes a GitHub release with
the zip and the user guide attached. Bump `\ProvidesPackage` in `tex/mathbb-one.sty` first.

## Licence

See [LICENSE](LICENSE). In short, the bbm sources say: "You may freely use, modify and/or distribute this file." The
fonts here are derived from them and are distributed on the same terms. `mathbb-one.sty` and
the build scripts are under the LPPL 1.3c.