URL: <https://savannah.gnu.org/bugs/?67244>
Summary: [devpdf,devps] special character `*m` should not
alias `mu`
Group: GNU roff
Submitter: gbranden
Submitted: Wed 25 Jun 2025 09:22:36 PM GMT
Category: Font - others/general
Severity: 3 - Normal
Item Group: Rendering/Cosmetics
Status: None
Privacy: Public
Assigned to: None
Open/Closed: Open
Discussion Lock: Any
Planned Release: None
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Follow-up Comments:
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Date: Wed 25 Jun 2025 09:22:36 PM GMT By: G. Branden Robinson <gbranden>
\[mu] and \[*m] should not be synonyms. The former is the "micro sign" and
should be upright. I observe this misbehavior as far back as _groff_ 1.22.3.
The latter is, in _troff_ tradition, a lowercase Greek letter mu for
mathematical applications, which means that it should be slanted.
Because the lowercase Greek letters supplied by PostScript's Symbol font are
upright, historically that device developed a slanted-symbol font "SS" to
provide these glyphs. Conventionally, that font is mounted prior to "S" in
the output device's "DESC" file. I think the reason for that is to ensure
that the character resolution process finds any special characters that are
"Greek" in the slanted symbol face before the unslanted one.
It's worth observing that in both _troff_ and PostScript, Symbol fonts are by
definition unstyled; they don't have "strong" or "heavy" (bold) or "oblique"
or "slanted" (italic) variants, or at least not in separate font files. Where
such variants exist, they have separate identities, encoded at different
indices in fonts and tend to get different code points in Unicode.
It is a historical accident that _troff_ made one choice about how "unstyled"
lowercase Greek letters should appear, and PostScript made another. Arguably,
PostScript's is more principled, whereas _troff_'s was more practical since
people typesetting mathematics want slanted lowercase Greek letters much more
commonly than upright ones.
The purpose of this ticket is only to fix the Greek lowercase mu; see
attachments.
But to resolve it we should also fix auxiliary files used in font generation
(like the map files _afmtodit_ uses), and _afmtodit_ itself, as necessary, to
ensure that this bug doesn't resurrect accidentally.
However in the longer term I think we can also arrange for the aforementioned
convention to be unnecessary. No "S" font should provide lowercase Greek
letters as _groff_ defines them (see _groff_char_(7)), and any "SS" font that
exists should provide **only** lowercase Greek letters.
Input:
$ cat ATTIC/greek-letters.groff
\Z'Greek\
\[*a]\[*b]\[*g]\[*d]\[*e]\[*z]\
\[*y]\[*h]\[*i]\[*k]\[*l]\[*m]\
\[*n]\[*c]\[*o]\[*p]\[*r]\[*s]\
\[*t]\[*u]\[*f]\[*x]\[*q]\[*o]\
\[+h]\[+p]\[+f]\[ts]'\
\l'16m\[ru]'
.\" Prior to groff 1.24, we need extra space or the output device name
.\" overprints the Greek letters. This is because the glyphs in groff's
.\" 1.24 font are scaled down from their upright counterparts (by 0.89),
.\" making a better match with groff's historical PostScript face.
.if '\?\*[.T]\?'\?pdf\?' \h'4m'
\*[.T]
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File Attachments:
-------------------------------------------------------
Name: greek-letters-1.22.3.ps Size: 7KiB
<https://file.savannah.gnu.org/file/greek-letters-1.22.3.ps?file_id=57328>
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Name: groff_lowercase_Greek_mu_is_wrongly_upright.png Size: 12KiB
<https://file.savannah.gnu.org/file/groff_lowercase_Greek_mu_is_wrongly_upright.png?file_id=57329>
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