*This post is a continuation of the investigation into
U+237C ⍼ RIGHT ANGLE WITH DOWNWARDS ZIGZAG ARROW. Many thanks to Barbara Beeton, James David Mason, Anders Berglund, David Bolton, and the Rare Books staff at the Cambridge University Library.*

## Where were we?

I’ve summarized a chronological timeline in the previous post,

but here are the highlights in reverse chronological,

corresponding roughly to the order in which I’ve discovered the information:

- ISO/IEC JTC1/SC2/WG2 N2191 (Proposal for Encoding Additional Mathematical Symbols)

adds U+237C ⍼ to the Unicode standard, which took characters from - The STIX project, whose character tables were compiled by Barbara Beeton,

taking characters from, among many other sources, - ISO/IEC TR 9573-13 (Public entity sets for mathematics and science), a technical report for SGML, where the trail ends.

Further investigation into various glyph registries and entity tables yielded no additional information.

About a year later, I went over everything I knew again and started looking for new leads.

The rest of this post collects together the live Twitter updates

I had been posting during this process.

## Who wrote TR 9573-13?

The ISO standards site tells us that TR 9573-13 was the responsibility of subcommittee 34 (SC 34)

under Joint Technical Committee 1 (JTC 1) of ISO/IEC.

A fortuitous search led to a historical account of JTC 1/SC34,

originally compiled by James David Mason, who was vice-chairman of SC 34.

Given the age of the document, I doubted the email address listed for him was up to date,

but eventually I found him on Linkedin, which indicated that he’s a co-chair for the Belisage Conference.

I contacted the conference chair, who put me in contact with Mason.

From the historical account and Mason himself,

I’ve found that working group 1 (WG 1) of SC 34 was responsible for ISO 8879, the SGML standard, as well as TR 9573-13.

The main people working on these were Charles Goldfarb, the inventor of SGML,

and Anders Berglund, who was responsible for TR 9573-13.

The entire SC 34 committee records

are now at the Charles Babbage Institute Archives at the University of Minnesota,

and consists of 9.5 cubic feet of material in 10 boxes (!).

Luckily, I wouldn’t have to fly to Minneapolis to sift through all of these records,

because eventually Mason managed to find me a current email address for Berglund.

## Where is TR 9573-13 from?

Berglund tells me that the entity sets for TR 9573-13 come from three sources:

- ISO/IEC 8859, a precursor of ISO/IEC 10646 and Unicode;
*MathSci, an expansion of mathfile, Appendix D*from the AMS; and- various typeface catalogues, notably Monotype.

Our glyph comes from Monotype under the matrix serial number S16139.

Unfortunately (but reasonably, as all of this is from three decades ago),

Berglund doesn’t have any notes on which Monotype catalogues were referenced.

However, I’ve separately confirmed that the symbol is indeed from Monotype from their archives.

Although the Type Archive,

which held the Monotype Collection, is now shutting down, the Science Museum Group has taken

photographs of the collection.

There are over 5000 punches and matrices

in the collection, but I was extremely lucky with my search keywords and happened upon a set of punches,

Extraneous sorts (L231)…

… which contains that very sort.

## Which Monotype catalogue is it in?

The SMG holds one catalogue, the *Specimen Book of ‘Monotype’ Printing Type*.

Its index

does list L231 as an “Extraneous sorts” series,

but those specimen sheets aren’t included in this book.

While looking for other catalogues that Monotype have published,

I came across Alembic Press’ collection

of Monotype publications.

I contacted David Bolton at the press for help with the catalogues,

who got back to me with a list of publications of lists of signs that do *not* contain S16139.

Since the serial number begins with S, it should be listed as a mathematical special sign,

but it was not found in any of:

*Monotype Special Sorts*(1931, 1947) — up to S1153, S6844;*Monotype Special Signs*(1954 – 1963) — up to S11819;*Monotype Mathematical Sorts List*(1956) — up to S10477;*4-Line Mathematics Classified List of Characters*(1967, 1970) — up to S19717, S20620.

Although the serial numbers in *4-Line Mathematics* do go past S16139,

it excludes several ranges such as S16137 – S16237 and S18325 – S18347,

likely characters not involved in 4-line mathematical typesetting

or were specialized commissioned characters.

Many signs were for individual customers, so might not merit being published in a list,

although for example I happen to have signs S2120 to S2125,

which were only for Jesus College Cambridge Boat Club as far as I know,

but which do feature in the 1947 list.

Alembic Press lists, but does not possess, one final document, *List of Mathematical Characters*.

However, it can be found in the Morison Collection

at the Cambridge University Library.

According to their catalogue, they have three documents under this name:

- [
**1970.11.585**] List of mathematical characters. London, 1970. 72p; ring bdg. [For

Monotype and Monophoto.] - [
**Morison.MC.D25**] List of mathematical characters. [London], nd. ca50 leaves - [
**1972.12.177**] List of mathematical characters. np, 1972. 21 loose sheets. [Sheets for

insertion in List (1970) .]

I contacted the Rare Books department, who have found two documents with this name.

The first is *List of mathematical characters: ‘Monotype’ 4-line Mathematics Series 569, ‘Monophoto’ Times Mathematics Series 569B* (1970).

The second is *L231 and L231B* (July 1972), a set of 21 sheets meant to be inserted at the end of the *List*.

Since S16139 was found in the set of punches of Extraneous Sorts in series L231,

I believe it must appear within these 21 sheets.

Unfortunately, as neither faculty nor a student at the University of Cambridge,

according to the quote they’ve given me,

requesting a digital copy of this document would cost 174£ (29 scans × 6£ each).

I’ve attempted to request it as an interlibrary loan,

but as archival material it can’t be requested this way.